U.S. patent number 5,986,028 [Application Number 08/980,140] was granted by the patent office on 1999-11-16 for elastic substantially linear ethlene polymers.
This patent grant is currently assigned to The Dow Chemical Company. Invention is credited to George W. Knight, Shih-Yaw Lai, James C. Stevens, John R. Wilson.
United States Patent |
5,986,028 |
Lai , et al. |
November 16, 1999 |
Elastic substantially linear ethlene polymers
Abstract
A continuous polymerization process of preparing ethylene
polymers containing less than about 20 ppm aluminum, and having
processability similar to highly branched low density polyethylene
(LDPE), but the strength and toughness of linear low density
polyethylene (LLDPE). The polymers have processing indices (PI's)
less than or equal to 70 percent of those of a comparative linear
ethylene polymer and a critical shear rate at onset of surface melt
fracture of at least 50 percent greater than the critical shear
rate at the onset of surface melt fracture of a traditional linear
ethylene polymer at about the same I.sub.2 and M.sub.w /M.sub.n.
The novel polymers can also have from about 0.01 to about 3 long
chain branches/1000 total carbons and have higher low/zero shear
viscosity and lower high shear viscosity than comparative linear
ethylene polymers. The novel polymers can also be characterized as
having a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63, a
molecular weight distribution, M.sub.w /M.sub.n, defined by the
equation: M.sub.w /M.sub.n .ltoreq.(I.sub.10 /I.sub.2)-4.63, a
critical shear stress at onset of gross melt fracture greater than
about 4.times.10.sup.6 dyne/cm.sup.2, and a single DSC melt peak
between -30 C. and 150 C.
Inventors: |
Lai; Shih-Yaw (Sugar Land,
TX), Wilson; John R. (Baton Rouge, LA), Knight; George
W. (Lake Jackson, TX), Stevens; James C. (Richmond,
TX) |
Assignee: |
The Dow Chemical Company
(Midland, MI)
|
Family
ID: |
46251600 |
Appl.
No.: |
08/980,140 |
Filed: |
November 26, 1997 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
455302 |
Aug 18, 1995 |
|
|
|
|
301948 |
Sep 7, 1994 |
|
|
|
|
166497 |
Dec 13, 1993 |
|
|
|
|
938281 |
Sep 2, 1992 |
5278272 |
|
|
|
301948 |
|
|
|
|
|
044426 |
Apr 7, 1993 |
|
|
|
|
776130 |
Oct 15, 1991 |
5272236 |
|
|
|
Current U.S.
Class: |
526/126; 526/131;
526/170; 526/901; 526/943 |
Current CPC
Class: |
B32B
27/08 (20130101); B32B 27/322 (20130101); C08F
10/00 (20130101); C08F 10/02 (20130101); C08F
210/16 (20130101); C08G 83/003 (20130101); C08J
5/18 (20130101); C08L 23/04 (20130101); C08L
23/0815 (20130101); C08L 23/16 (20130101); B29C
48/15 (20190201); B29C 48/022 (20190201); C08F
10/00 (20130101); C08F 4/6592 (20130101); C08F
10/00 (20130101); C08F 4/6192 (20130101); C08F
210/16 (20130101); C08F 4/6592 (20130101); C08L
23/04 (20130101); C08L 23/0815 (20130101); C08L
23/16 (20130101); B29K 2995/0022 (20130101); C08F
4/61908 (20130101); C08F 4/61912 (20130101); C08F
4/6192 (20130101); C08F 4/65908 (20130101); C08F
4/65912 (20130101); C08F 4/6592 (20130101); C08F
110/00 (20130101); C08F 110/02 (20130101); C08J
2303/08 (20130101); C08J 2323/04 (20130101); C08J
2323/08 (20130101); C08L 23/02 (20130101); C08L
23/06 (20130101); C08L 2205/02 (20130101); C08L
2314/06 (20130101); Y10S 526/943 (20130101); Y10S
526/901 (20130101); B29C 48/00 (20190201); B29C
48/08 (20190201); B29C 48/10 (20190201); C08L
2666/04 (20130101); C08L 2666/04 (20130101); C08L
2666/04 (20130101); C08F 110/02 (20130101); C08F
2500/08 (20130101); C08F 2500/09 (20130101); C08F
2500/11 (20130101); C08F 2500/12 (20130101); C08F
2500/05 (20130101); C08F 110/02 (20130101); C08F
2500/12 (20130101); C08F 2500/19 (20130101); C08F
2500/11 (20130101); C08F 110/02 (20130101); C08F
2500/12 (20130101); C08F 2500/07 (20130101); C08F
2500/03 (20130101); C08F 2500/19 (20130101); C08F
2500/17 (20130101); C08F 210/16 (20130101); C08F
210/14 (20130101); C08F 2500/12 (20130101); C08F
2500/17 (20130101); C08F 2500/09 (20130101); C08F
2500/03 (20130101); C08F 2500/26 (20130101); C08F
210/16 (20130101); C08F 210/14 (20130101); C08F
2500/19 (20130101); C08F 2500/12 (20130101); C08F
2500/17 (20130101); C08F 2500/09 (20130101); C08F
2500/03 (20130101); C08F 210/16 (20130101); C08F
210/14 (20130101); C08F 2500/08 (20130101); C08F
2500/11 (20130101); C08F 2500/03 (20130101); C08F
2500/09 (20130101); C08F 210/16 (20130101); C08F
210/14 (20130101); C08F 2500/12 (20130101); C08F
2500/19 (20130101); C08F 2500/11 (20130101); C08F
210/16 (20130101); C08F 210/14 (20130101); C08F
2500/12 (20130101); C08F 2500/09 (20130101); C08F
2500/11 (20130101); C08F 2500/19 (20130101); C08F
2500/03 (20130101); C08F 210/16 (20130101); C08F
210/14 (20130101); C08F 2500/03 (20130101); C08F
2500/09 (20130101); C08F 2500/08 (20130101); C08F
2500/12 (20130101); C08F 2500/26 (20130101); C08F
210/16 (20130101); C08F 2500/12 (20130101); C08F
2500/09 (20130101); C08F 2500/11 (20130101); C08F
2500/19 (20130101); C08F 2500/03 (20130101); C08F
210/16 (20130101); C08F 210/14 (20130101); C08F
2500/26 (20130101) |
Current International
Class: |
B29C
47/00 (20060101); C08G 83/00 (20060101); B29C
47/02 (20060101); B32B 27/08 (20060101); B32B
27/32 (20060101); C08F 10/00 (20060101); C08F
10/02 (20060101); C08J 5/18 (20060101); C08F
210/00 (20060101); C08L 23/04 (20060101); C08L
23/00 (20060101); C08L 23/08 (20060101); C08L
23/16 (20060101); C08F 210/16 (20060101); C08F
4/6192 (20060101); C08F 4/00 (20060101); C08F
4/659 (20060101); C08F 4/619 (20060101); C08F
110/00 (20060101); C08F 4/6592 (20060101); C08F
110/02 (20060101); C08L 23/02 (20060101); C08F
002/04 (); C08F 002/18 (); C08F 002/34 () |
Field of
Search: |
;526/126,131,170,901,943 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2008315 |
|
Jul 1990 |
|
CA |
|
0416815A2 |
|
Mar 1991 |
|
EP |
|
85/04664 |
|
Oct 1985 |
|
WO |
|
9003414 |
|
Apr 1990 |
|
WO |
|
94/07930 |
|
Apr 1994 |
|
WO |
|
Other References
Derwent 90-239017/31 (1990). .
Journal of Polymer Science. Part A, vol, 1 (pp. 2869-2880 (1963)),
"Long-Chain Branching Frequency in Polyethylene" by J. E. Guillet.
.
Polymer Preprints, Amer.Chem.Society, vol. 12, No. 1, pp. 277-281
(Mar. 1971), "Evidence of Long-Chain Branching in High Density
Polyethylene" by E. E. Drott and R. A. Mendelson. .
Journal of the American Chemical Society, 98:7, pp. 1729-1742 (Mar.
31, 1976) "Structure and Chemistry of Bis(cyclopentadienyl)-MLn
Complexes" by Joseph W.Lauher and Roald Hoffman. .
Polymer Engineering and Science, vol. 16, No. 12, pp. 811-816 (Dec.
1976), "Influence of Long-Chain Branching on the Viscoelastic
Properties of Low-Density Polyethylenes" by L. Wild, R. Ranganath,
and D. Knobeloch. .
Angew. Chem. Int. Ed. Engl, pp. 630-632 (1976) vol. 15, No. 10,
"Halogen-Free Soluble Ziegler Catalysts for the Polymerization of
Ethylene. Control of Molecular Weight by Choice of Temperature
Temperature" by Arne Andresen et al. .
Advances in Organometallic Chemistry, pp. 99-148, vol. 18, (1980)
"Ziegler-Natta Catalysis" by Hansjorg Sinn and Walter Kaminsky.
.
Angew. Chem. Int. Ed. Engl., pp. 390-393, vol. 19 No. 5 (1980)
"`Living Polymers` on Polymerization with Extremely Productive
Ziegler Catalysts" by Hansjorg Sinn, Walter Kaminsky, Hans-Jurgen
Vollmer, and Rudiger Woldt. .
Polymer Bullentin, 9, pp. 464-469 (1983) "Halogen Free Soluble
Ziegler Catalysts with Methylalumoxan as Cataylst" by Jens Herwig
and Walter Kaminsky. .
Makromol. Chem. Rapid Commun., 4, pp. 417-421 (1983)
"Bis(cyclopentadienyl)zirkon-Verbingungen und Aluminoxan als
Ziegler-Katalysatoren fur die Polymerisation und Copolymerisation
von Olefinen" by Walter Kaminsky et al. .
ANTEC Proceedings, pp. 306-309 (1983), "Analysis of Long Chain
Branching in High Density Polyethylene" by J.K. Hughes. .
Makromol. Chem., Rapid Commun., (5) pp. 225-2285 (1984) "Influence
of hydrogen on the polymerization of ethylene with the homogeneous
Ziegler system
bis(cyclopentadienyl)zirconiumdicholoride/aluminoxane" by Walter
Kaminsky et al. .
Journal of Polymer Science: Polymer Chemistry Edition, pp.
2117-2133 (1985), vol. 23, "Homogenous Ziegler-Natta Catalysis II.
Ethylene Polymerization by IVB Transaction Metal Complexes/Methyl
Aluminoxane Catalyst Systems" by Giannetti and R. Mazzochi. .
Journal of Applied Polymer Science, pp. 3751-3765 (1985) vol. 30,
"On the Effects of Very Low Levels of Long Chain Branching on
Rheological Behavior in Polyethylene" by B.H. Bersted. .
Journal of Polymer Science: Polymer Chemistry Edition, pp.
2151-2164 (1985) vol. 23, "Ethylene Propylene Diene Terpolymers
Produced with a Homogeneous and Highly Active Zirconium Catalyst"
by Walter Kaminsky et al. .
The Society of Rheology, pp. 337-357 (1986) vol. 30, "Wall Slip in
Viscous Fluids and Influence of Materials of Construction" by A. V.
Ramamurthy. .
Makromol. Chem., Macromol. Symp., 4, pp. 103-118 (1986) "Elastomers
By Atactic Linkage of .alpha.Olefins Using Soluble Ziegler
Catalysts" by W. Kaminsky and M. Schlobohm. .
Journal of Rheology, 31 (8) pp. 815-834 (1987) "Wall Slip and
Extrudate Distortion in Linear Low-Density Polyethylene" by D.
Kalika and M. Denn. .
Journal of Macromolecular Science: Reviews in Macromolecular
Chemistry and Physics.C29 (2&3), pp. 201-303 (1989) "A Review
of High Resolution Liquid .sup.13 C arbon Nuclear Magnetic
Resonance Characterizations of Ethylene-Based Polymers". .
Journal of Non-Newtonian Fluid Mechanics, 36, pp. 255-263 (1990)
"Additional Observations on The Surface Melt Fracture Behavior of
Linear Low-Density Polyethylene" by R. Moynihan, D. Baird, and R.
Ramanathan. .
Makromol. Chem. Rapid Commun., pp. 89-94 (1990) "Terpolymers of
Ethylene, Propene and 1,5-Hexadiene Synthesized with
Zirconocene/Methylaluminoxane" by W. Kaminsky and H. Drogemuller.
.
Journal of Rheology, 35, (4) ,3 (May, 1991) pp. 497-52, "Wall Slip
of Molten HIgh Density Polyethylene. I.Sliding Plate Rheometer
Studies" by S. G. Hatzikiriakos and J. M. Dealy. .
Proceedings of the 1991 IEEE Power Engineering Society, pp. 184-190
(Sep. 22-27, 1991), "New Specialty Linear Polymers (SLP) For Power
Cables" by Monica Hendewerk and Lawrence Spenadel. .
Society of Plastic Engineers Proceedings, Polyolefins VII
International Conference, Feb. 24-27, 1991, Structure/Poperty
Relationships In Exxpo# Polymers (pp. 45-66) by C. Speed, B.
Trudell, A. Mehta, and F. Stehling. .
1991 Specialty Polyolefins Conference Proceedings, "The Marketing
Challenge Created By Single Site Catalysts in Polyolefins," Sep.
24, 1991, (pp. 41-45) by Michael P. Jeffries. .
High Polymers, vol. XX, "Crystalline Olefin Polymers" Part 1, pp.
495-501. .
1991 Polymers Laminations & Coatings Conference, TAPPI
Proceedings, presented in Feb., 1991, pp. 289-296, "A New Family of
Linear Ethylene Polymers with Enhanced Sealing Performance" by D.
Van der Sanden and R. W. Halle. .
Society of Plastic Engineers 1991 Specialty Polyolefins Conference
Proceedings, pp. 41-55, "The Marketing Challenge Created by Single
Site Catalysts in Polyolefins" by M. Jefferies (Sep. 24, 1991).
.
Advances in Polyolefins, by R. B. Seymour and T. Cheng, (1987) pp.
373-380 "Crystallinity and Morphology of Ethylene/.alpha.-Olefin
Copolymers" by P. Schouterden, G. Groeninckx, and H. Reynaers.
.
Advances In Polyolefins, by R.B. Seymour and T. Cheng, (1987) "New
Catalysis and Process For Ethylene Polymerization", pp. 337-354, by
F. Karol, B. Wagner, L. Levine, G. Goeke, and A. Noshay. .
Advances in Polyolefins, by R. B. Seymour and T. Cheng, (1987)
"Polymerization of Olefins With A Homogeneous Zirconium/Alumoxane
Catalyst", pp. 361-371 by W. Kaminsky and H. Hahnsen. .
Yang et al. "Cation-like Homogeneus Olefin Polymerization Catalysts
Based upon Zirconocene Alkyls and Tris(pentafluorophenyl)borane",
J. Am. Chem. Soc. pp. 3623-3625 1991..
|
Primary Examiner: Wu; David W.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This is a continuation of application Ser. No. 08/455,302 filed on
Aug. 18, 1995, now abandoned, which is a divisional Ser. No.
08/301,948 filed on Sep. 7, 1994, now abandoned which is a
continuation-in-part of U.S. application Ser. No. 08/044,426 filed
Apr. 7, 1993, now U.S. Pat. No. 5,320,810 which is a divisional of
U.S. application Ser. No. 07/776,130 filed Oct. 15, 1991, now U.S.
Pat. No. 5,272,236. Application Ser. No. 08/455,302 is also a
continuation-in-part of U.S. application Ser. No. 08/166,497 filed
Dec. 13, 1993, now abandoned which is a divisional of U.S.
application Ser. No. 07/939,281 filed Sep. 2, 1992 which is now
U.S. Pat. No. 5,278,272.
Claims
We claim:
1. A continuous polymerization process of preparing an ethylene
polymer containing less than about 20 ppm aluminum, and having (i)
a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63, (ii) a
molecular weight distribution, M.sub.w /M.sub.n, defined by the
equation: M.sub.w /M.sub.n .ltoreq.(I.sub.10 /I.sub.2)-4.63, (iii)
an average of about 0.01 to about 3 long chain branches/1000 total
carbons, and (iv) a critical shear stress at onset of gross melt
fracture of greater than about 4.times.10.sup.6 dyne/cm.sup.2, said
process characterized by continuously contacting in a
polymerization reactor a reactant selected from the group
consisting of ethylene alone and ethylene and one or more C.sub.3
-C.sub.20 alpha-olefins, with a catalyst composition under
continuous steady state polymerization conditions, wherein said
catalyst composition is characterized as:
(a) A metal coordination complex corresponding to the formula:
##STR8## wherein: M is a metal of group 3-10, or the Lanthanide
series of the Periodic Table of the Elements;
R' each occurrence is independently selected from the group
consisting of hydrogen, alkyl, aryl, silyl, germyl, cyano, halo and
combinations thereof having up to 20 non-hydrogen atoms;
Z is a moiety comprising boron, or a member of group 14 of the
Periodic Table of the Elements, and optionally sulfur or oxygen,
said moiety having up to 20 non-hydrogen atoms;
X independently each occurrence is an anionic ligand group or
neutral Lewis base ligand group having up to 30 non-hydrogen
atoms;
n is 0, 1, 2, 3 or 4 and is 2 less than the valence of M; and
Y is an anionic or nonanionic ligand group bonded to Z and M
comprising nitrogen, phosphorus, oxygen or sulfur and having up to
20 non-hydrogen atoms, optionally Y and Z together form a fused
ring system, and
(b) an activating cocatalyst.
2. The process of claim 1 wherein the polymerization temperature is
from 20 C to 250 C, wherein the ethylene concentration is from 6.7
to 12.5 percent by weight of the reactor contents, and wherein the
concentration of the ethylene polymer is less than 5 percent by
weight of the reactor contents.
3. The process of claim 2 wherein the ethylene concentration is
further characterized as not more than 8 percent of the reactor
contents to form an ethylene polymer having a I.sub.10 /I.sub.2 of
at least about 8.
4. The process of claim 1 wherein (a) is an amidosilane or
amidoalaediyl compound corresponding to the formula: ##STR9##
wherein: M is titanium, zirconium or hafnium, bound in an eta.sup.5
bonding mode to the cyclopentadienyl group;
R' each occurrence is independently selected from the group
consisting of hydrogen, silyl, alkyl, aryl and combinations thereof
having up to 10 carbon or silicon atoms;
E is silicon or carbon;
X independently each occurrence is hydride, halo, alkyl, aryl,
aryloxy or alkoxy of up to 10 carbons;
m is 1 or 2; and
n is 1 or 2.
5. The process of claim 1 or 4 in which component b) is an inert,
noncoordinating boron cocatalyst.
6. The process of claim 1 or 4 in which the cocatalyst is
trispentafluorophenyl)borane.
7. The process of claim 1 or 4 wherein the process is:
(A) a gas phase process,
(B) a suspension process,
(C) a solution process, or
(D) a slurry process.
8. The process of claim 7 wherein the polymerization conditions
comprise a reaction temperature and ethylene concentration
sufficient to form an ethylene polymer having a I.sub.10 /I.sub.2
of at least about 8.
Description
FIELD OF THE INVENTION
This invention relates to elastic substantially linear ethylene
polymers having improved processability, e.g., low susceptibilty to
melt fracture, even under high shear stress conditions. Such
substantially linear ethylene polymers have a critical shear rate
at the onset of surface melt fracture substantially higher than,
and a processing index substantially less than, that of a linear
polyethylene at the same molecular weight distribution and melt
index.
BACKGROUND OF THE INVENTION
Molecular weight distribution (MWD), or polydispersity, is a well
known variable in polymers. The molecular weight distribution,
sometimes described as the ratio of weight average molecular weight
(M.sub.w) to number average molecular weight (M.sub.n) (i.e.,
M.sub.w /M.sub.n) can be measured directly, e.g., by gel permeation
chromatography techniques, or more routinely, by measuring I.sub.10
/I.sub.2 ratio, as described in ASTM D-1238. For linear
polyolefins, especially linear polyethylene, it is well known that
as M.sub.w /M.sub.n increases, I.sub.10 /I.sub.2 also
increases.
John Dealy in "Melt Rheology and Its Role in Plastics Processing"
(Van Nostrand Reinhold, 1990) page 597 discloses that ASTM D-1238
is employed with different loads in order to obtain an estimate of
the shear rate dependence of melt viscosity, which is sensitive to
weight average molecular weight (M.sub.w) and number average
molecular weight (M.sub.n).
Bersted in Journal of Applied Polymer Science Vol. 19, page
2167-2177 (1975) theorized the relationship between molecular
weight distribution and steady shear melt viscosity for linear
polymer systems. He also showed that the broader MWD material
exhibits a higher shear rate or shear stress dependency.
Ramamurthy in Journal of Rheology, 30(2), 337-357 (1986), and
Moynihan, Baird and Ramanathan in Journal of Non-Newtonian Fluid
Mechanics, 36, 255-263 (1990), both disclose that the onset of
sharkskin (i.e., surface melt fracture) for linear low density
polyethylene (LLDPE) occurs at an apparent shear stress of
1-1.4.times.10.sup.6 dyne/cm.sup.2, which was observed to be
coincident with the change in slope of the flow curve. Ramamurthy
also discloses that the onset of surface melt fracture or of gross
melt fracture for high pressure low density polyethylene (HP-LDPE)
occurs at an apparent shear stress of about 0.13 MPa
(1.3.times.10.sup.6 dyne/cm). Ramamurthy also discloses that "the
corresponding shear stresses (0.14 and 0.43 MPa) for linear
polyethylenes are widely separated." However, these LLDPE resins
are linear resins, and are believed to be those made by Union
Carbide in their UNIPOL process (which uses conventional
Ziegler-Natta catalysis which results in a heterogeneous comonomer
distribution). The LLDPE is reported in Tables I and II to have a
broad M.sub.w /M.sub.n of 3.9. The melt fracture tests conducted by
Ramamurthy were in the temperature range of 190 to 220 C.
Furthermore, Ramamurthy reports that the onset of both surface and
gross melt fracture (for LLDPE resins) are ". . . essentially
independent of MI (or molecular weight), melt temperature, die
diameter (0.5-2.5 mm), die length/diameter ratio (2-20), and the
die entry angle (included angle: 60-180 degrees)."
Kalika and Denn in Journal of Rheology, 31, 815-834 (1987)
confirmed the surface defects or sharkskin phenomena for LLDPE, but
the results of their work determined a critical shear stress at
onset of surface melt fracture of 0.26 MPa, significantly higher
than that found by Ramamurthy and Moynihan et al. Kalika and Denn
also report that the onset of gross melt fracture occurs at 0.43
MPa which is consistent with that reported by Ramamurthy. The LLDPE
resin tested by Kalika and Denn was an antioxidant-modified (of
unknown type) UNIPOL LLDPE having a broad M.sub.w /M.sub.n of 3.9.
Kalika and Denn performed their melt fracture tests at 215 C.
However, Kalika and Denn seemingly differ with Ramamurthy in the
effects of their L/D of the rheometer capillary. Kalika and Denn
tested their LLDPE at L/D's of 33.2, 66.2, 100.1, and 133.1 (see
Table 1 and FIGS. 5 and 6).
International Patent Application (Publication No. WO 90/03414)
published Apr. 5, 1990 to Exxon Chemical Company, discloses linear
ethylene interpolymer blends with narrow molecular weight
distribution and narrow short chain branching distributions
(SCBDs). The melt processibility of the interpolymer blends is
controlled by blending different molecular weight interpolymers
having different narrow molecular weight distributions and
different SCBDs.
Exxon Chemical Company, in the Preprints of Polyolefins VII
International Conference, page 45-66, February 24-27 1991, disclose
that the narrow molecular weight distribution (NMWD) resins
produced by their EXXPOL.TM. technology have higher melt viscosity
and lower melt strength than conventional Ziegler resins at the
same melt index. In a recent publication, Exxon Chemical Company
has also taught that NMWD polymers made using a single site
catalyst create the potential for melt fracture ("New Specialty
Linear Polymers (SLP) For Power Cables," by Monica Hendewerk and
Lawrence Spenadel, presented at IEEE meeting in Dallas, Tex.,
September, 1991). In a similar vein, in "A New Family of Linear
Ethylene Polymers Provides Enhanced Sealing Performance" by Dirk G.
F. Van der Sanden and Richard W. Halle, (February 1992 Tappi
Journal), Exxon Chemical Company has also taught that the molecular
weight distribution of a polymer is described by the polymers melt
index ratio (i.e., I.sub.10 /I.sub.2) and that their new narrow
molecular weight distribution polymers made using a single site
catalyst are "linear backbone resins containing no functional or
long chain branches."
U.S. Pat. No. 5,218,071 (Canadian patent application 2,008,315-A)
to Mitsui Petrochemical Industries, Ltd., teaches ethylene
copolymers composed of structural units (a) derived from ethylene
and structural units (b) derived from alpha-olefins of 3-20 carbons
atoms, said ethylene copolymers having [A] a density of 0.85-0.92
g/cm.sup.3, [B] an intrinsic viscosity as measured in decalin at
135 C of 0.1-10 dl/g, [C] a ratio (M.sub.w /M.sub.n) of a weight
average molecular weight (M.sub.w) to a number average molecular
weight (M.sub.n) as measured by GPC of 1.2-4, and [D] a ratio
(MFR.sub.10 /MFR.sub.2) of MFR.sub.10 under a load of 10 kg to
MFR.sub.2 under a load of 2.16 kg at 190 C of 8-50, and being
narrow in molecular weight distribution and excellent in
flowability. However, the ethylene copolymers of U.S. Pat. No. '071
are made with a catalysis system composed of methylaluminoxane and
ethylenebis(indenyl)hafnium dichloride (derived from HfCl.sub.4
containing 0.78% by weight of zirconium atoms as contaminates). It
is well known that mixed metal atom catalyst species (such as
hafnium and zirconium in U.S. Pat. No. '071) polymerizes copolymer
blends, which are evidence by multiple melting peaks. Such
copolymer blends therefore are not homogeneous in terms of their
branching distribution.
WO 85/04664 to BP Chemicals Ltd. teaches a process for the
thermo-mechanical treatment of copolymers of ethylene and higher
alpha-olefins of the linear low density polyethylene type with at
least one or more organic peroxides to produce copolymers that are
particularly well suited for extrusion or blow-molding into hollow
bodies, sheathing, and the like. These treated copolymers show an
increased flow parameter (I.sub.21 /I.sub.2) without significantly
increasing the M.sub.w /M.sub.n. However, the novel polymers of the
present invention have long chained branching and obtained this
desirable result without the need of a peroxide treatment.
U.S. Pat. No. 5,096,867 discloses various ethylene polymers made
using a single site catalyst in combinations with methyl
aluminoxane. These polymers, in particular Example 47, have
extremely high levels of aluminum resulting from catalyst residue.
When these aluminum residues are removed from the polymer, the
polymer exhibits gross melt fracture at a critical shear stress of
less than 4.times.10.sup.6 dyne/cm.sup.2.
All of the foregoing patents, applications, and articles are herein
incorporated by reference.
Previously known narrow molecular weight distribution linear
polymers disadvantageously possessed low shear sensitivity or low
I.sub.10 /I.sub.2 value, which limits the extrudability of such
polymers. Additionally, such polymers possessed low melt
elasticity, causing problems in melt fabrication such as film
forming processes or blow molding processes (e.g., sustaining a
bubble in the blown film process, or sag in the blow molding
process etc.). Finally, such resins also experienced melt fracture
surface properties at relatively low extrusion rates thereby
processing unacceptably.
SUMMARY OF THE INVENTION
A new class of homogeneous ethylene polymers have now been
discovered which have long chain branching and unusual but
desirable bulk properties. These new polymers include both
homopolymers of ethylene and interpolymers of ethylene and at least
one alpha-olefin. Both the homo- and interpolymers have long chain
branching, but the interpolymers have short chain branching in
addition to the long chain branching. The short chain branches are
the residue of the alpha-olefins that are incorporated into the
polymer backbone or in other words, the short chain branches are
that part of the alpha-olefin not incorporated into the polymer
backbone. The length of the short chain branches is two carbon
atoms less than the length of the alpha-olefin comonomer. The short
chain branches are randomly, ie. uniformily, distributed throughout
the polymer as opposed to heterogeneously branched
ethylene/alpha-olefin interpolymers such as conventional Zeigler
LLDPE.
These novel ethylene polymers have a shear thinning and ease of
processability similar to highly branched low density polyethylene
(LDPE), but with the strength and toughness of linear low density
polyethylene (LLDPE). These novel ethylene polymers can also be
characterized as "substantially linear" polymers, whereby the bulk
polymer has an average of up to about 3 long chain branches/1000
total carbons or in other words, at least some of the polymer
chains have long chain branching. The novel substantially linear
ethylene polymers are distinctly different from traditional Ziegler
polymerized heterogeneous polymers (e.g., LLDPE) and are also
different from traditional free radical/high pressure polymerized
LDPE. Surprisingly, the novel substantially linear ethylene
polymers are also different from linear homogeneous ethylene
polymers having a uniform comonomer distribution, especially with
regard to processability.
These novel ethylene polymers, especially those with a density
greater than or equal to about 0.9 g/cm.sup.3 are characterized as
having:
a) a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63,
b) a molecular weight distribution, M.sub.w /M.sub.n, defined by
the equation:
c) a critical shear stress at onset of gross melt fracture greater
than about 4.times.10.sup.6 dyne/cm.sup.2, and
d) a single melt peak as determined by differential scanning
calorimetry (DSC) between -30 and 150 C.
The novel ethylene polymers can also be characterized as
having:
a) a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63,
b) a molecular weight distribution, M.sub.w /M.sub.n, defined by
the equation:
c) a critical shear rate at onset of surface melt fracture at least
50 percent greater than the critical shear rate at the onset of
surface melt fracture of a linear ethylene polymer with an I.sub.2,
M.sub.w /M.sub.n, and density each within ten percent of the novel
ethylene polymer, and
d) a single melt peak as determined by differential scanning
calorimetry (DSC) between -30 and 150 C.
In another aspect, the novel ethylene polymers, especially those
having a density greater than or equal to about 0.9 g/cm.sup.3, are
characterized as having:
a) a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63, and
b) a molecular weight distribution, M.sub.w /M.sub.n of from about
1.5 to about 2.5,
c) a critical shear stress at onset of gross melt fracture greater
than about 4.times.10.sup.6 dyne/cm.sup.2, and
d) a single melt peak as determined by differential scanning
calorimetry (DSC) between -30 and 150 C.
In still another aspect, the novel ethylene polymers are
characterized as having:
a) a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63,
b) a molecular weight distribution, M.sub.w /M.sub.n of from about
1.5 to about 2.5,
c) a critical shear rate at onset of surface melt fracture of at
least 50 percent greater than the critical shear rate at the onset
of surface melt fracture of a linear ethylene polymer with an
I.sub.2, M.sub.w /M.sub.n, and density each within ten percent of
the novel ethylene polymer, and
d) a single melt peak as determined by differential scanning
calorimetry (DSC) between -30 and 150 C.
The substantially linear ethylene polymers can also be
characterized as having a critical shear rate at onset of surface
melt fracture of at least 50 percent greater than the critical
shear rate at the onset of surface melt fracture of a linear
ethylene polymer having an I.sub.2, M.sub.w /M.sub.n and density
each within ten percent of the substantially linear ethylene
polymer.
In still another aspect the novel polymer can be characterized as a
substantially linear ethylene bulk polymer having:
(a) and average of about 0.01 to about 3 long chain branches/1000
total carbons,
(b) a critical shear stress at onset of gross melt fracture of
greater than about 4.times.10.sup.6 dyne/cm.sup.2, and
(c) a single DSC melt peak between -30 and 150 C.
The substantially linear ethylene bulk polymer can also be
characterized as having:
(a) an average of about 0.01 to about 3 long chain branches/1000
total carbons,
(b) a critical shear rate at onset of surface melt fracture of at
least 50 percent greater than the critical shear rate at the onset
of surface melt fracture of a linear ethylene polymer having an
I.sub.2, M.sub.w /M.sub.n and density each within ten percent of
the substantially linear ethylene bulk polymer, and
(c) a single DSC melt peak between -30 and 150 C.
In still another aspect, the ethylene polymer can be characterized
as a substantially linear ethylene bulk polymer having:
(a) an average of about 0.01 to about 3 long chain branches/1000
total carbons,
(b) a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63,
(c) a molecular weight distribution, M.sub.w /M.sub.n, from about
1.5 to about 2.5, and
(d) a single DSC melt peak between -30 and 150 C.
The novel ethylene polymers, especially the substantially linear
ethylene polymers, also have a processing index (PI) less than or
equal to about 70 percent of the PI of a linear ethylene polymer at
about the same I.sub.2, M.sub.w /M.sub.n, and density each within
ten percent of the novel ethylene polymer.
Compositions comprising the novel ethylene polymer and at least one
other natural or synthetic polymer are also within the scope of the
invention.
Elastic substantially linear ethylene polymers comprising ethylene
homopolymers or an interpolymer of ethylene with at least one
C.sub.3 -C.sub.20 alpha-olefin copolymers are especially
preferred.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a polymerization process
suitable for making the polymers of the present invention.
FIG. 2 plots data describing the relationship between I.sub.10
/I.sub.2 and M.sub.w /M.sub.n for two examples of the invention,
and for some comparative examples.
FIG. 3 plots the shear stress versus shear rate for an Example of
the invention and for a Comparative Example, described herein.
FIG. 4 plots the shear stress versus shear rate for an Example of
the invention and for a Comparative Example, described herein.
FIG. 5 plots the heat seal strength versus heat seal temperature of
film made from Examples of the invention, and for Comparative
Examples, described herein.
FIG. 6 graphically displays dynamic shear viscosity data for an
elastic substantially linear ethylene polymer of the present
invention and for a comparative linear polymer made using single
site catalyst technology.
FIG. 7 graphically displays I.sub.10 /I.sub.2 ratio as a function
of ethylene concentration in the polymerization reactor for
ethylene/propene substantially linear copolymers of the
invention.
FIG. 8 graphically displays the melting curves for a comparative
polymer made according to U.S. Pat. No. 5,218,071 (Mitsui).
FIG. 9 graphically displays the structural characteristics of a
traditional heterogeneous Ziegler polymerized LLDPE copolymers, a
highly branched high pressure-free radical LDPE, and a novel
substantially linear ethylene/alpha-olefin copolymer of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
The term "linear" as used herein means that the ethylene polymer
does not have long chain branching. That is, the polymer chains
comprising the bulk linear ethylene polymer have an absence of long
chain branching, as for example the traditional linear low density
polyethylene polymers or linear high density polyethylene polymers
made using Ziegler polymerization processes (e.g., U.S. Pat. No.
4,076,698 (Anderson et al.)), sometimes called heterogeneous
polymers. The term "linear" does not refer to bulk high pressure
branched polyethylene, ethylene/vinyl acetate copolymers, or
ethylene/vinyl alcohol copolymers which are known to those skilled
in the art to have numerous long chain branches. The term "linear"
also refers to polymers made using uniform branching distribution
polymerization processes, sometimes called homogeneous polymers,
including narrow MWD (e.g. about 2) made using single site
catalysts. Such uniformly branched or homogeneous polymers include
those made as described in U.S. Pat. No. 3,645,992 (Elston) and
those made using so-called single site catalysts in a batch reactor
having relatively high ethylene concentrations (as described in
U.S. Pat. No. 5,026,798 (Canich) or in U.S. Pat. No. 5,055,438
(Canich)) or those made using constrained geometry catalysts in a
batch reactor also having relatively high olefin concentrations (as
described in U.S. Pat. No. 5,064,802 (Stevens et al.) or in EP 0
416 815 A2 (Stevens et al.)). The uniformly branched/homogeneous
polymers are those polymers in which the comonomer is randomly
distributed within a given interpolymer molecule or chain, and
wherein substantially all of the interpolymer molecules have the
same ethylene/comonomer ratio within that interpolymer, but these
polymers too have an absence of long chain branching, as, for
example, Exxon Chemical has taught in their February 1992 Tappi
Journal paper. For example, FIG. 9 shows the structural differences
among conventional heterogeneously branched LLDPE, homogeneously
branched linear LLDPE, highly branched high pressure, free radical
LDPE, and the homogeneously branched substantially linear ethylene
polymers of the present invention.
The term "substantially linear" as used means that the bulk polymer
is substituted, on average, with about 0.01 long chain
branches/1000 total carbons (including both backbone and branch
carbons) to about 3 long chain branches/1000 total carbons.
Preferred polymers are substituted with about 0.01 long chain
branches/1000 total carbons to about 1 long chain branches/1000
total carbons, more preferably from about 0.05 long chain
branches/1000 total carbons to about 1 long chain branched/1000
total carbons, and especially from about 0.3 long chain
branches/1000 total carbons to about 1 long chain branches/1000
total carbons.
As used herein, the term "backbone" refers to a discrete molecule,
and the term "polymer" or "bulk polymer" refers in the conventional
sense to the polymer as formed in a reactor. For the polymer to be
a "substantially linear" polymer, the polymer must have at least
enough molecules with long chain branching such that the average
long chain branching in the bulk polymer is at least an average of
about 0.01/1000 total carbons.
The term "bulk polymer" means the polymer which results from the
polymerization process and, for the substantially linear polymers,
includes molecules having both an absence of long chain branching,
as well as molecules having long chain branching. Thus a "bulk
polymer" includes all molecules formed during polymerization. It is
understood that, for the substantially linear polymers, not all
molecules have long chain branching, but a sufficient amount do
such that the average long chain branching content of the bulk
polymer positively affects the melt rheology (i.e., the melt
fracture properties).
Long chain branching (LCB) is defined herein as a chain length of
at least one (1) carbon less than the number of carbons in the
comonomer, whereas short chain branching (SCB) is defined herein as
a chain length of the same number of carbons in the residue of the
comonomer after it is incorporated into the polymer molecule
backbone. For example, an ethylene/1-octene substantially linear
polymer has backbones with long chain branches of at least seven
(7) carbons in length, but it also has short chain branches of only
six (6) carbons in length.
Long chain branching can be distinguished from short chain
branching by using .sup.13 C nuclear magnetic resonance (NMR)
spectroscopy and to a limited extent, e.g. for ethylene
homopolymers, it can be quantified using the method of Randall
(Rev. Macromol. Chem. Phys., C29 (2& 3), p. 285-297), the
disclosure of which is incorporated herein by reference. However as
a practical matter, current .sup.13 C nuclear magnetic resonance
spectroscopy cannot determine the length of a long chain branch in
excess of about six (6) carbon atoms and as such, this analytical
technique cannot distinguish between a seven (7) carbon branch and
a seventy (70) carbon branch. The long chain branch can be as long
as about the same length as the length of the polymer backbone.
U.S. Pat. No. 4,500,648, incorporated herein by reference, teaches
that long chain branching frequency (LCB) can be represented by the
equation LCB=b/M.sub.w wherein b is the weight average number of
long chain branches per molecule and M.sub.w is the weight average
molecular weight. The molecular weight averages and the long chain
branching characteristics are determined by gel permeation
chromatography and intrinsic viscosity methods.
Similar to the traditional homogeneous polymers, the substantially
linear ethylene/alpha-olefin copolymers of the invention have only
a single melting point, as opposed to traditional Ziegler
polymerized heterogeneous linear ethylene/alpha-olefin copolymers
which have two or more melting points (determined using
differential scanning calorimetry (DSC)). Ethylene polymers of this
invention are also characterized by a single DSC melting peak
between -30 and 150C. However, those polymers having a density of
about 0.875 g/cm.sup.3 to about 0.91 g/cm.sup.3, the single melt
peak may show, depending on equipment sensitivity, a "shoulder" or
a "hump" on the low side of the melting peak (i.e. below the
melting point) that constitutes less than 12 percent, typically,
less than 9 percent, more typically less than 6 percent of the
total heat of fusion of the polymer. This artifact is due to
intrapolymer chain variations, and it is discerned on the basis of
the slope of the single melting peak varying monotonically through
the melting region of the artifact. Such artifact occurs within 34
C, typically within 27 C, and more typically within 20 C of the
melting point of the single melting peak. The single melting peak
is determined using a differential scanning calorimeter
standardized with indium and deionized water. The method involves
about 5-7 mg sample sizes, a "first heat" to about 150 C which is
held for 4 minutes, a cool down at 10/min. to -30 C which is held
for 3 minutes, and heat up at 10 C/min. to 150 C for the "second
heat" heat flow vs. temperature curve. Total heat of fusion of the
polymer is calculated from the area under the curve. The heat of
fusion attributable to this artifact, if present, can be determined
using an analytical balance and weight-percent calculations.
FIG. 8 displays the melting curves for a polymer of the invention
and for a comparative polymer as described in U.S. Pat. No.
5,218,071 (Mitsui). Note that the comparative polymer has two
melting peaks (the high melting peak with a shoulder on its high
side, i.e. above the second melting point), and this is indicative
of the presence of two distinct polymers (as opposed to the melting
curve of the invention polymer having only a single melting
peak).
The SCBDI (Short Chain Branch Distribution Index) or CDBI
(Composition Distribution Branch Index) is defined as the weight
percent of the polymer molecules having a comonomer content within
50 percent of the median total molar comonomer content. The CDBI of
a polymer is readily calculated from data obtained from techniques
known in the art, such as, for example, temperature rising elution
fractionation (abbreviated herein as "TREF") as described, for
example, in Wild et al, Journal of Polymer Science, Poly. Phys.
Ed., Vol. 20, p. 441 (1982), or as described in U.S. Pat. No.
4,798,081. The SCBDI or CDBI for the substantially linear ethylene
polymers of the present invention is typically greater than about
30 percent, preferably greater than about 50 percent, more
preferably greater than about 80 percent, and most preferably
greater than about 90 percent.
"Melt tension" is measured by a specially designed pulley
transducer in conjunction with the melt indexer. Melt tension is
the load that the extrudate or filament exerts while passing over
the pulley onto a two inch drum that is rotating at the standard
speed of 30 rpm. The melt tension measurement is similar to the
"Melt Tension Tester" made by Toyoseiki and is described by John
Dealy in "Rheometers for Molten Plastics", published by Van
Nostrand Reinhold Co. (1982) on page 250-251. The melt tension of
these new polymers is also surprisingly good, e.g., as high as
about 2 grams or more. For the novel substantially linear ethylene
interpolymers of this invention, especially those having a very
narrow molecular weight distribution (i.e., M.sub.w /M.sub.n from
1.5 to 2.5), the melt tension is typically at least about 5
percent, and can be as much as about 60 percent, greater than the
melt tension of a conventional linear ethylene interpolymer having
a melt index, polydispersity and density each within ten percent of
the substantially linear ethylene polymer.
A unique characteristic of the presently claimed polymers is a
highly unexpected flow property where the I.sub.10 /I.sub.2 value
is essentially independent of polydispersity index (i.e. M.sub.w
/M.sub.n). This is contrasted with conventional Ziegler polymerized
heterogeneous polyethylene resins and with conventional single site
catalyst polymerized homogeneous polyethylene resins having
Theological properties such that as the polydispersity index
increases, the I.sub.10 /I.sub.2 value also increases.
The density of the neat ethylene or substantially linear ethylene
polymers of this invention, i.e. polymers without inorganic fillers
and not containing in excess of 20 ppm aluminum from catalyst
residue, is measured in accordance with ASTM D-792. The ethylene or
substantially linear ethylene polymers are crystalline and/or
semi-crystalline polymers, are normally solid at room temperature,
and are pelletizable at ambient conditions or at temperatures
induced by cooled water. For example, a novel substantially linear
ethylene/1-octene copolymer having a density of 0.865 g/cm.sup.3
has about 10% crystallinity at room temperature. The minimum
density is typically at least about 0.865 g/cm.sup.3, preferably at
least about 0.870 g/cm.sup.3, and more preferably at least about
0.900 g/cm.sup.3. The maximum density typically does not exceed
about 0.970 g/cm.sup.3, preferably it does not exceed about 0.940
g/cm.sup.3, and more preferably it does not exceed about 0.92
g/cm.sup.3.
The molecular weight of the ethylene or ethylene/alpha-olefin
substantially linear ethylene polymers in the present invention is
conveniently indicated using a melt index measurement according to
ASTM D-1238, Condition 190 C/2.16 kg (formally known as "Condition
(E)" and also known as 12). Melt index is inversely proportional to
the molecular weight of the polymer. Thus, the higher the molecular
weight, the lower the melt index, although the relationship is not
linear. The melt index for the ethylene or ethylene/alpha-olefin
substantially linear ethylene polymers used herein is generally
from about 0.01 grams/10 minutes (g/10 min) to about 1000 g/10 min,
preferably from about 0.01 g/10 min to about 100 g/10 min, and
especially from about 0.01 g/10 min to about 10 g/10 min.
Another measurement useful in characterizing the molecular weight
of the substantially linear ethylene polymers is conveniently
indicated using a melt index measurement according to ASTM D-1238,
Condition 190C/10 kg (formerly known as "Condition (N)" and also
known as I.sub.10). The ratio of these two melt index terms is the
melt flow ratio and is designated as I.sub.10 /I.sub.2. For the
substantially linear ethylene/alpha-olefin polymers of the
invention, the I.sub.10 /I.sub.2 ratio indicates the degree of long
chain branching, i.e., the higher the I.sub.10 /I.sub.2 ratio, the
more long chain branching in the polymer. Generally, the I.sub.10
/I.sub.2 ratio of the substantially linear ethylene/alpha-olefin
polymers is at least about 5.63, preferably at least about 7,
especially at least about 8, most especially at least about 9 or
above. The only limitations on the maximum I.sub.10 /I.sub.2 ratio
are practical considerations such as economics, polymerization
kinetics, etc., but typically the maximum I.sub.10 /I.sub.2 ratio
does not exceed about 20, and preferably it does not exceed about
15.
Antioxidants (e.g., hindered phenolics (e.g., Irganox.RTM. 1010
made by Ciba Geigy Corp.), phosphites (e.g., Irgafos.RTM. 168 made
by Ciba Geigy Corp.)), are preferably added to protect the polymer
from degradation during thermal processing steps such as
pelletization, molding, extrusion, and characterization methods.
Other additives to serve special functional needs include cling
additives, e.g. PIB, antiblocks, antislips, pigments, fillers.
In-process additives, e.g. calcium stearate, water, etc., may also
be used for other purposes such as for the deactivation of residual
catalyst. However, peroxide need not be added to the novel polymers
in order for the polymers to exhibit an I.sub.10 /I.sub.2
independent of the MWD and the melt fracture properties.
Molecular Weight Distribution Determination
The whole interpolymer product samples and the individual
interpolymer samples are analyzed by gel permeation chromatography
(GPC) on a Waters 150 C high temperature chromatographic unit
equipped with three linear mixed porosity bed columns (available
from Polymer Laboratories), operating at a system temperature of
140 C. The solvent is 1,2,4-trichlorobenzene, from which 0.3
percent by weight solutions of the samples are prepared for
injection. The flow rate is 1.0 milliliters/minute and the
injection size is 200 microliters.
The molecular weight determination is deduced by using narrow
molecular weight distribution polystyrene standards (from Polymer
Laboratories) in conjunction with their elution volumes. The
equivalent polyethylene molecular weights are determined by using
appropriate Mark-Houwink coefficients for polyethylene and
polystyrene (as described by Williams and Ward in Journal of
Polymer Science, Polymer Letters, Vol. 6, (621) 1968) to derive the
following equation:
In this equation, a=0.4316 and b=1.0 for polyethylene and
polystyrene in 1,2,4-trichlorobenzene. Weight average molecular
weight, M.sub.w, is calculated in the usual manner according to the
following formula: M.sub.w =.epsilon.w.sub.i *M.sub.i, where
w.sub.i and M.sub.i are the weight fraction and molecular weight,
respectively, of the it fraction eluting from the GPC column.
The molecular weight distribution (M.sub.w /M.sub.n) for the
substantially linear ethylene polymers of the invention is
generally less than about 5, preferably from about 1.5 to about
2.5, and especially from about 1.7 to about 2.3.
Processing Index Determination
The "rheological processing index" (PI) is the apparent viscosity
(in kpoise) of a polymer and is measured by a gas extrusion
rheometer (GER). The GER is described by M. Shida, R. N. Shroff and
L. V. Cancio in Polym. Eng. Sci., Vol. 17, no. 11, p. 770 (1977),
and in "Rheometers for Molten Plastics" by John Dealy, published by
Van Nostrand Reinhold Co. (1982) on page 97-99, the disclosures of
both of which are incorporated in their entirety herein by
reference. The processing index is measured at a temperature of 190
C, at nitrogen pressure of 2500 psig using a 0.0296 inch (752
micrometers) diameter (preferably 0.0143 inch diameter die for high
flow polymers, e.g. 50-100 melt index or greater), 20:1 L/D die
having an entrance angle of 180 degrees. The GER processing index
is calculated in millipoise units from the following equation:
where:
2.5.times.10.sup.6 dyne/cm.sup.2 is the shear stress at 2500 psi,
and the shear rate is the shear rate at the wall as represented by
the following equation:
where:
Q' is the extrusion rate (gms/min),
0.745 is the melt density of polyethylene (gm/cm.sup.3), and
Diameter is the orifice diameter of the capillary (inches).
The PI is the apparent viscosity of a material measured at apparent
shear stress of 2.5.times.10.sup.6 dyne/cm.sup.2.
For the substantially linear ethylene polymers (or
ethylene/alpha-olefin copolymers or interpolymers), the PI is less
than or equal to 70 percent of that of a conventional linear
ethylene polymer (or ethylene/alpha-olefin copolymer or
interpolymer) having an I.sub.2, M.sub.w /M.sub.n and density each
within ten percent of the substantially linear ethylene
polymer.
An apparent shear stress vs. apparent shear rate plot is used to
identify the melt fracture phenomena over a range of nitrogen
pressures from 5250 to 500 psig using the die or GER test apparatus
previously described. According to Ramamurthy in Journal of
Rheology, 30(2), 337-357, 1986, above a certain critical flow rate,
the observed extrudate irregularities may be broadly classified
into two main types: surface melt fracture and gross melt
fracture.
Surface melt fracture occurs under apparently steady flow
conditions and ranges in detail from loss of specular gloss to the
more severe form of "sharkskin". In this disclosure, the onset of
surface melt fracture is characterized at the beginning of losing
extrudate gloss at which the surface roughness of extrudate can
only be detected by 40.times. magnification. The critical shear
rate at onset of surface melt fracture for the substantially linear
ethylene polymers is at least 50 percent greater than the critical
shear rate at the onset of surface melt fracture of a linear
ethylene polymer having about the same I.sub.2 and M.sub.w
/M.sub.n. Preferably, the critical shear stress at onset of surface
melt fracture for the substantially linear ethylene polymers of the
invention is greater than about 2.8.times.10.sup.6
dyne/cm.sup.2.
Gross melt fracture occurs at unsteady flow conditions and ranges
in detail from regular (alternating rough and smooth, helical,
etc.) to random distortions. For commercial acceptability, (e.g.,
in blown film products), surface defects should be minimal, if not
absent. The critical shear rate at onset of surface melt fracture
(OSMF) and critical shear stress at onset of gross melt fracture
(OGMF) will be used herein based on the changes of surface
roughness and configurations of the extrudates extruded by a GER
For the substantially linear ethylene polymers of the invention,
the critical shear stress at onset of gross melt fracture is
preferably greater than about 4.times.10.sup.6 dyne/cm.sup.2.
For the processing index determination and for the GER melt
fracture determination, the novel ethylene or substantially linear
ethylene copolymers are tested without inorganic fillers, and they
do not have more than 20 ppm aluminum catalyst residue. Preferably,
however, for the processing index and melt fracture tests, the
novel ethylene polymers and substantially linear ethylene
copolymers do contain antioxidants such as phenols, hindered
phenols, phosphites or phosphonites, preferably a combination of a
phenol or hindered phenol and a phosphite or a phosphonite.
The Constrained Geometry Catalyst
Suitable constrained geometry catalysts for use herein preferably
include constrained geometry catalysts as disclosed in U.S.
application Ser. Nos.: 545,403, filed Jul. 3, 1990; 758,654, filed
Sep. 12, 1991 (now U.S. Pat. No. 5,132,380); 758,660, filed Sep.
12, 1991; and 720,041, filed Jun. 24, 1991 now abandoned. The
monocyclopentadienyl transition metal olefin polymerization
catalysts taught in U.S. Pat. No. 5,026,798 which is incorporated
herein by reference, are also believed to be suitable for use in
preparing the polymers of the present invention, so long as the
polymerization conditions substantially conform to those.
The foregoing catalysts may be further described as comprising a
metal coordination complex comprising a metal of groups 3-10 or the
Lanthanide series of the Periodic Table of the Elements and a
delocalized Pi-bonded moiety substituted with a constrain-inducing
moiety, said complex having a constrained geometry about the metal
atom such that the angle at the metal between the centroid of the
delocalized, substituted pi-bonded moiety and the center of at
least one remaining substituent is less than such angle in a
similar complex containing a similar pi-bonded moiety lacking in
such constrain-inducing substituent, and provided further that for
such complexes comprising more than one delocalized, substituted
pi-bonded moiety, only one thereof for each metal atom of the
complex is a cyclic, delocalized, substituted pi-bonded moiety. The
catalyst further comprises an activating cocatalyst.
Preferred catalyst complexes correspond to the formula: ##STR1##
wherein: M is a metal of group 3-10, or the Lanthanide series of
the Periodic Table of the Elements;
Cp* is a cyclopentadienyl or substituted cyclopentadienyl group
bound in an eta.sup.5 bonding mode to M;
Z is a moiety comprising boron, or a member of group 14 of the
Periodic Table of the Elements, and optionally sulfur or oxygen,
said moiety having up to 20 non-hydrogen atoms, and optionally Cp*
and Z together form a fused ring system;
X independently each occurrence is an anionic ligand group or
neutral Lewis base ligand group having up to 30 non-hydrogen
atoms;
n is 0, 1, 2, 3, or 4 and is 2 less than the valence of M; and
Y is an anionic or nonanionic ligand group bonded to Z and M
comprising nitrogen, phosphorus, oxygen or sulfur and having up to
20 non-hydrogen atoms, optionally Y and Z together form a fused
ring system.
More preferably still, such complexes correspond to the formula:
##STR2## wherein: R' each occurrence is independently selected from
the group consisting of hydrogen, allyl, aryl silyl, germyl, cyano,
halo and combinations thereof having up to 20 non-hydrogen
atoms;
X each occurrence independently is selected from the group
consisting of hydride, halo, alkyl, aryl, silyl germyl, aryloxy,
alkoxy, amide, siloxy, neutral Lewis base ligands and combinations
thereof having up to 20 non-hydrogen atoms;
Y is --O--, --S--, --NR*--, --PR*--, or a neutral two electron
donor ligand selected from the group consisting of OR*, SR*,
NR*.sub.2 or PR*.sub.2 ;
M is as previously defined; and
Z is SiR*.sub.2, CR*.sub.2, SiR*.sub.2, CR*.sub.2 CR*.sub.2,
CR*.dbd.CR*, CR*.sub.2 SiR*.sub.2, GeR*.sub.2, BR*, BR*.sub.2 ;
wherein
R* each occurrence is independently selected from the group
consisting of hydrogen, alkyl, aryl, silyl, halogenated alkyl,
halogenated aryl groups having up to 20 non-hydrogen atoms, and
mixtures thereof, or two or more R* groups from Y, Z, or both Y and
Z form a fused ring system; and n is 1 or 2.
It should be noted that whereas formula I and the following
formulas indicate a cyclic structure for the catalysts, when Y is a
neutral two electron donor ligand, the bond between M and Y is more
accurately referred to as a coordinate-covalent bond. Also, it
should be noted that the complex may exist as a dimer or higher
oligomer.
Further preferably, at least one of R', Z, or R* is an electron
donating moiety. Thus, highly preferably Y is a nitrogen or
phosphorus containing group corresponding to the formula --N(R")--
or --P(R")--, wherein R" is C.sub.1-10 alkyl or aryl, i.e., an
amido or phosphido group.
Most highly preferred complex compounds are amidosilane- or
amidoalkanediyl-compounds corresponding to the formula: ##STR3##
wherein: M is titanium, zirconium or hafnium, bound in an eta.sup.5
bonding mode to the cyclopentadienyl group;
R' each occurrence is independently selected from the group
consisting of hydrogen, silyl, alkyl, aryl and combinations thereof
having up to 10 carbon or silicon atoms;
E is silicon or carbon;
X independently each occurrence is hydride, halo, alkyl, aryl,
aryloxy or alkoxy of up to 10 carbons;
m is 1 or 2; and
n is 1 or 2.
Examples of the above most highly preferred metal coordination
compounds include compounds wherein the R' on the amido group is
methyl, ethyl propyl, butyl pentyl hexyl (including isomers),
norbomyl, benzyl, phenyl, etc.; the cyclopentadienyl group is
cyclopentadienyl indenyl, tetrahydroindenyl, fluorenyl,
octahydrofluorenyl, etc.; R' on the foregoing cyclopentadienyl
groups each occurrence is hydrogen, methyl, ethyl, propyl, butyl,
pentyl hexyl (including isomers), norbomyl benzyl phenyl etc.; and
X is chloro, bromo, iodo, methyl ethyl propyl, butyl, pentyl,
hexyl, (including isomers), norbomyl benzyl phenyl, etc. Specific
compounds include: (tert-butylamido)(tetramethyl-eta.sup.5
-cyclopentadienyl)-1,2-ethanediylzirconium dichloride,
(tert-butylamido)(tetramethyl-eta.sup.5
-cyclopentadienyl)-1,2-ethanediyltitanium dichloride,
(methylamido)(tetramethyl-eta.sup.5
-cyclopentadienyl)-1,2-ethanediylzirconium dichloride,
(methylamido)(tetramethyl-eta.sup.5
-cyclopentadienyl)-1,2-ethanediyltitanium dichloride,
(ethylamido)(tetramethyl-eta.sup.5
-cyclopentadienyl)-methylenetitanium dichloro,
(tertbutylamido)dibenzyl(tetramethyl-eta.sup.5 -cyclopentadienyl)
silanezirconium dibenzyl,
(benzylamido)dimethyl-(tetramethyl-eta.sup.5
-cyclopentadienyl)silanetitanium dichloride,
(phenylphosphido)dimethyl(tetramethyl-eta.sup.5
-cyclopentadienyl)silanezirconium dibenzyl,
(tertbutylamido)dimethyl(tetramethyl-eta.sup.5
-cyclopentadienyl)silanetitanium dimethyl, and the like.
The complexes may be prepared by contacting a derivative of a
metal, M, and a group I metal derivative or Grignard derivative of
the cyclopentadienyl compound in a solvent and separating the salt
byproduct. Suitable solvents for use in preparing the metal
complexes are aliphatic or aromatic liquids such as cyclohexane,
methylcyclohexane, pentane, hexane, heptane, tetrahydrofuran,
diethyl ether, benzene, toluene, xylene, ethylbenzene, etc., or
mixtures thereof.
In a preferred embodiment, the metal compound is MX.sub.n+1, i.e.,
M is in a lower oxidation state than in the corresponding compound,
MX.sub.n+2 and the oxidation state of M in the desired final
complex. A noninterfering oxidizing agent may thereafter be
employed to raise the oxidation state of the metal. The oxidation
is accomplished merely by contacting the reactants utilizing
solvents and reaction conditions used in the preparation of the
complex itself. By the term "noninterfering oxidizing agent" is
meant a compound having an oxidation potential sufficient to raise
the metal oxidation state without interfering with the desired
complex formation or subsequent polymerization processes. A
particularly suitable noninterfering oxidizing agent is AgCl or an
organic halide such as methylene chloride. The foregoing techniques
are disclosed in U.S. Ser. Nos.: 545,403, filed Jul. 3, 1990 and
702,475, filed May 20, 1991, the teachings of both of which are
incorporated herein by reference.
Additionally the complexes may be prepared according to the
teachings of the copending U.S. application Ser. No. 778,433
entitled: "Preparation of Metal Coordination Complex (I)", filed in
the names of Peter Nickias and David Wilson, on Oct. 15, 1991 now
abandoned and the copending U.S. application Ser. No. 778,432
entitled: "Preparation of Metal Coordination Complex (II)", filed
in the names of Peter Nickias and David Devore, on Oct. 15, 1991,
now abandoned and the patents issuing therefrom, all of which are
incorporated herein by reference.
Suitable cocatalysts for use herein include polymeric or oligomeric
aluminoxanes, especially methyl aluminoxane, as well as inert,
compatible, noncoordinating, ion forming compounds. So called
modified methyl aluminoxane (MMAO) is also suitable for use as a
cocatalyst. One technique for preparing such modified aluminoxane
is disclosed in U.S. Pat. No. 5,041,584. Aluminoxanes can also be
made as disclosed in U.S. Pat. Nos. 5,218,071; 5,086,024,
5,041,585, 5,041,583, 5,015,749, 4,960,878 and 4,544,762 all of
which are incorporated herein by reference. Aluminoxanes, including
modified methyl aluminoxanes, when used in the polymerization, are
preferably used such that preferably less than about 20 ppm
aluminum, especially less than about 10 ppm aluminum, and more
preferably less than about 5 ppm aluminum, from catalyst residue
remain in the polymer. In order to measure the bulk polymer
properties (e.g. PI or melt fracture), aqueous HCl is used to
extract the aluminoxane from the polymer. Preferred cocatalysts,
however, are inert, noncoordinating, boron compounds such as those
described in EP 520732 which is incorporated herein by
reference.
Ionic active catalyst species which can be used to polymerize the
polymers described wherein correspond to the formula: ##STR4##
wherein: M is a metal of group 3-10, or the Lanthanide series of
the Periodic Table of the Elements;
Cp* is a cyclopentadienyl or substituted cyclopentadienyl group
bound in an eta.sup.5 bonding mode to M;
Z is a moiety comprising boron, or a member of group 14 of the
Periodic Table of the Elements, and optionally sulfur or oxygen,
said moiety having up to 20 non-hydrogen atoms, and optionally Cp*
and Z together form a fused ring system;
X independently each occurrence is an anionic ligand group or
neutral Lewis base ligand group having up to 30 non-hydrogen
atoms;
n is 0, 1, 2, 3, or 4 and is 2 less than the valence of M; and
A- is a noncoordinating, compatible anion.
One method of making the ionic catalyst species which can be
utilized to make the polymers of the present invention involve
combining:
a) at least one first component which is a mono(cyclopentadienyl)
derivative of a metal of Group 3-10 or the Lanthanide Series of the
Periodic Table of the Elements containing at least one substituent
which will combine with the cation of a second component (described
hereinafter) which first component is capable of forming a cation
formally having a coordination number that is one less than its
valence, and
b) at least one second component which is a salt of a Bronsted acid
and a noncoordinating, compatible anion.
More particularly, the non-coordinating, compatible anion of the
Bronsted acid salt may comprise a single coordination complex
comprising a charge-bearing metal or metalloid core, which anion is
both bulky and non-nucleophilic. The recitation "metalloid", as
used herein, includes non-metals such as boron, phosphorus and the
like which exhibit semi-metallic characteristics.
Illustrative, but not limiting examples of monocyclopentadienyl
metal components (first components) which may be used in the
preparation of cationic complexes are derivatives of titanium,
zirconium, vanadium, hafium, chromium, lanthanum, etc. Preferred
components are titanium or zirconium compounds. Examples of
suitable monocyclopentadienyl metal compounds are
hydrocarbyl-substituted monocyclopentadienyl metal compounds such
as (tert-butylamido)(tetramethyl-eta.sup.5
-cyclopentadienyl)-1,2-ethanediylzirconium dimethyl,
(tert-butylamido)(tetramethyl-eta.sup.5
-cyclopentadienyl)-1,2-thanediyltitanium dimethyl,
(methylamido)(tetramethyl-eta.sup.5
-cyclopentadienyl)-1,2-ethanediylzirconium dibenzyl,
(methylamido)(tetramethyl-eta.sup.5
-cyclopentadienyl)-1,2-ethanediyltitanium dimethyl (ethylamido)
(tetramethyl-eta.sup.5 -cyclopentadienyl) methylenetitanium
dimethyl, (tertbutylamido)dibenzyl(tetramethyl-eta.sup.5
-cyclopentadienyl) silanezirconium dibenzyl,
(benzylamido)dimethyl-(tetramethyl-eta.sup.5
-cyclopentadienyl)silanetitanium diphenyl,
(phenylphosphido)dimethyl(tetramethyl-eta.sup.5
-cyclopentadienyl)silanezirconium dibenzyl, and the like.
Such components are readily prepared by combining the corresponding
metal chloride with a dilithium salt of the substituted
cyclopentadienyl group such as a cyclopentadienyl-alkanediyl,
cyclopentadienyl--silane amide, or cyclopentadienyl--phosphide
compound. The reaction is conducted in an inert liquid such as
tetrahydrofuran, C.sub.5-10 alkanes, toluene, etc. utilizing
conventional synthetic procedures. Additionally, the first
components may be prepared by reaction of a group II derivative of
the cyclopentadienyl compound in a solvent and separating the salt
by-product Magnesium derivatives of the cyclopentadienyl compounds
are preferred. The reaction may be conducted in an inert solvent
such as cyclohexane, pentane, tetrahydrofuran, diethyl ether,
benzene, toluene, or mixtures of the like. The resulting metal
cyclopentadienyl halide complexes may be alkylated using a variety
of techniques. Generally, the metal cyclopentadienyl alkyl or aryl
complexes may be prepared by alkylation of the metal
cyclopentadienyl halide complexes with alkyl or aryl derivatives of
group I or group II metals. Preferred alkylating agents are alkyl
lithium and Grignard derivatives using conventional synthetic
techniques. The reaction may be conducted in an inert solvent such
as cyclohexane, pentane, tetrahydrofuran, diethyl ether, benzene,
toluene, or mixtures of the like. A preferred solvent is a mixture
of toluene and tetrahydrofuran.
Compounds useful as a second component in the preparation of the
ionic catalysts useful in this invention will comprise a cation,
which is a Bronsted acid capable of donating a proton, and a
compatible noncoordinating anion. Preferred anions are those
containing a single coordination complex comprising a
charge-bearing metal or metalloid core which anion is relatively
large (bulky), capable of stabilizing the active catalyst species
(the Group 3-10 or Lanthanide Series cation) which is formed when
the two components are combined and sufficiently labile to be
displaced by olefinic, diolefinic and acetylenically unsaturated
substrates or other neutral Lewis bases such as ethers, nitriles
and the like. Suitable metals, then, include, but are not limited
to, aluminum, gold, platinum and the like. Suitable metalloids
include, but are not limited to, boron, phosphorus, silicon and the
like. Compounds containing anions which comprise coordination
complexes containing a single metal or metalloid atom are, of
course, well known and many, particularly such compounds containing
a single boron atom in the anion portion, are available
commercially. In light of this, salts containing anions comprising
a coordination complex containing a single boron atom are
preferred.
Highly preferably, the second component useful in the preparation
of the catalysts of this invention may be represented by the
following general formula:
wherein:
L is a neutral Lewis base;
(L-H)+ is a Bronsted acid; and
[A]- is a compatible, noncoordinating anion.
More preferably [A]- corresponds to the formula:
wherein:
M' is a metal or metalloid selected from Groups 5-15 of the
Periodic Table of the Elements; and
Q independently each occurrence is selected from the Group
consisting of hydride, dialkylamido, halide, alkoxide, aryloxide,
hydrocarbyl, and substituted-hydrocarbyl radicals of up to 20
carbons with the proviso that in not more than one occurrence is Q
halide and
q is one more than the valence of M'.
Second components comprising boron which are particularly useful in
the preparation of catalysts of this invention may be represented
by the following general formula:
wherein:
L is a neutral Lewis base;
[L-H]+ is a Bronsted acid;
B is boron in a valence state of 3; and
Q is as previously defined.
Illustrative, but not limiting, examples of boron compounds which
may be used as a second component in the preparation of the
improved catalysts of this invention are trialkyl-substituted
ammonium salts such as triethylammonium tetraphenylborate,
tripropylammonium tetraphenylborate, tris(n-butyl)ammonium
tetraphenylborate, trimethylammonium tetrakis(p-tolyl)borate,
triethylammonium tetrakis(pentafluorophenyl)borate,
tripropylammonium tetrakis(2,4-dimethylphenyl)borate,
triethylammonium tetrakis(3,5-dimethylphenyl)borate,
triethylammonium tetralis(3,5-di-trifluoromethylphenyl)borate and
the like. Also suitable are N,N-dialkyl anilinium salts such as
N,N-dimethyl-aniliniumtetraphenylborate, N,N-diethylanilinium
tetraphenylborate, N,N-2,4,6-pentamethylanilinium tetraphenylborate
and the like; dialkylammonium salts such as di-(i-propyl)ammonium
tetrakis(pentafluorophenyl)borate, dicyclohexylammonium
tetraphenylborate and the like; and triaryl phosphonium salts such
as triphenylphosphonium tetraphenylborate,
tri(methylphenyl)phosphonium tetrakis-pentafluorophenylborate,
tri(dimethylphenyl)phosphonium tetraphenylborate and the like.
Preferred ionic catalysts are those having a limiting charge
separated structure corresponding to the formula: ##STR5## wherein:
M is a metal of group 3-10, or the Lanthanide series of the
Periodic Table of the Elements;
Cp* is a cyclopentadienyl or substituted cyclopentadienyl group
bound in an eta.sup.5 bonding mode to M;
Z is a moiety comprising boron, or a member of group 14 of the
Periodic Table of the Elements, and optionally sulfur or oxygen,
said moiety having up to 20 non-hydrogen atoms, and optionally Cp*
and Z together form a fused ring system;
X independently each occurrence is an anionic ligand group or
neutral Lewis base ligand group having up to 30 non-hydrogen
atoms;
n is 0, 1, 2, 3, or 4 and is 2 less than the valence of M; and
XA*-- is --XB(C.sub.6 F.sub.5).sub.3.
This class of cationic complexes may be conveniently prepared by
contacting a metal compound corresponding to the formula: ##STR6##
wherein: Cp*, M, and n are as previously defined,
with tris(pentafluorophenyl)borane cocatalyst under conditions to
cause abstraction of X and formation of the anion --XB(C.sub.6
F.sub.5).sub.3.
Preferably X in the foregoing ionic catalyst is C.sub.1 -C.sub.10
hydrocarbyl, most preferably methyl.
The preceding formula is referred to as the limiting, charge
separated structure. However, it is to be understood that,
particularly in solid form, the catalyst may not be fully charge
separated. That is, the X group may retain a partial covalent bond
to the metal atom, M. Thus, the catalysts may be alternately
depicted as possessing the formula: ##STR7##
The catalysts are preferably prepared by contacting the derivative
of a Group 4 or Lanthanide metal with the
tris(pentafluorophenyl)borane in an inert diluent such as an
organic liquid.
Tris(pentafluorphenyl)borane is a commonly available Lewis acid
that may be readily prepared according to known techniques. The
compound is disclosed in Marks, et al. J. Am. Chem. Soc. 1991, 113,
3623-3625 for use in alkyl abstraction of zirconocenes.
All reference to the Periodic Table of the Elements herein shall
refer to the Periodic Table of the Elements, published and
copyrighted by CRC Press, Inc., 1989. Also, any reference to a
Group or Groups shall be to the Group or Groups as reflected in
this Periodic Table of the Elements using the IUPAC system for
numbering groups.
It is believed that in the constrained geometry catalysts used
herein the metal atom is forced to greater exposure of the active
metal site because one or more substituents on the single
cyclopentadienyl or substituted metal is both bonded to an adjacent
covalent moiety and held in association with the cyclopentadienyl
group through an eta.sup.5 or other pi-bonding interaction. It is
understood that each respective bond between the metal atom and the
constituent atoms of the cyclopentadienyl or substituted
cyclopentadienyl group need not be equivalent. That is, the metal
may be symmetrically or unsymmetrically pi-bound to the
cyclopentadienyl or substituted cyclopentadienyl group.
The geometry of the active metal site is further defined as
follows. The centroid of the cyclopentadienyl or substituted
cyclopentadienyl group may be defined as the average of the
respective X, Y, and Z coordinates of the atomic centers forming
the cyclopentadienyl or substituted cyclopentadienyl group. The
angle, theta, formed at the metal center between the centroid of
the cyclopentadienyl or substituted cyclopentadienyl group and each
other ligand of the metal complex may be easily calculated by
standard techniques of single crystal X-ray diffraction. Each of
these angles may increase or decrease depending on the molecular
structure of the constrained geometry metal complex. Those
complexes wherein one or more of the angles, theta, is less than in
a similar, comparative complex differing only in the fact that the
constrain inducing substituent is replaced by hydrogen, have
constrained geometry for purposes of the present invention.
Preferably one or more of the above angles, theta, decrease by at
least 5 percent, more preferably 7.5 percent, compared to the
comparative complex. Highly preferably, the average value of all
bond angles, theta, is also less than in the comparative
complex.
Preferably, monocyclopentadienyl metal coordination complexes of
group 4 or lanthanide metals according to the present invention
have constrained geometry such that the smallest angle, theta,
between the centroid of the Cp* group and the Y substituent, is
less than 115 degrees, more preferably less than 110 degrees, most
preferably less than 105 degrees, and especially less than 100
degrees.
Other compounds which are useful in the catalyst compositions of
this invention, especially compounds containing other Group 4 or
Lanthanide metals, will, of course, be apparent to those skilled in
the art.
Polymerization
The improved melt elasticity and processibility of the
substantially linear polymers according to the present invention
result, it is believed, from their method of production. The
polymers may be produced via a continuous (as opposed to a batch)
controlled polymerization process using at least one reactor (e.g.,
as disclosed in WO 93/07187, WO 93/07188, and WO 93/07189, the
disclosures of each of which is incorporated herein by reference),
but can also be produced using multiple reactors (e.g., using a
multiple reactor configuration as described in U.S. Pat. No.
3,914,342, the disclosure of which is incorporated herein by
reference) at a polymerization temperature and pressure sufficient
to produce the interpolymers having the desired properties.
While not wishing to be bound by any particular theory, the
inventors believe that long chain branches are formed in their
novel polymers according to the following sequence:
Propagation Step
Termination Step
Copolymerization
Continued Polymerization
Termination Step
wherein:
R=growing polymer chain
R'=long chain branch (LCB), and
R"=growing polymer chain after insertion of R".
In polymerizing ethylene and ethylene/alpha-olefin copolymers, a
batch reactor process typically operates at an ethylene
concentration from about 6.7 to about 12.5 percent by weight of the
reactor contents and have a polymer concentration generally less
than about 5 percent by weight of the reactor contents, dependent
upon the ethylene solubility, which is a function of reactor
diluent, temperature and pressure. The initial polymer
concentration is zero and increases over time as the reaction
proceeds such that the highest polymer concentration occurs at the
end of the reaction, the point at which the catalyst is spent. Most
of the polymer is made during the initial minutes of the
polymerization.
According to one embodiment of the present process, the polymers
are produced in a continuous process operated at a steady state
(i.e. the reactants are fed to the reactor at a rate in
substantially in balance with the rate that product is removed from
the reactor such that the reaction mass in the reactor is
relatively constant in volume and composition), as opposed to a
batch process. Preferably, the polymerization temperature of the
continuous process is from about 20 C to about 250 C, using
constrained geometry catalyst technology. If a narrow molecular
weight distribution polymer (M.sub.w /M.sub.n of from about 1.5 to
about 2.5) having a higher I.sub.10 /I.sub.2 ratio (e.g. I.sub.10
/I.sub.2 of 7 or more, preferably at least 8, especially at least 9
and as high as about 20 or more) is desired, the ethylene
concentration in the reactor is preferably not more than about 8
percent by weight of the reactor contents, especially not more than
about 6 percent by weight of the reactor contents, and most
especially not more than about 4 percent by weight of the reactor
contents, and as low as about 0.75 percent by weight of the reactor
contents. Preferably, the polymerization is performed in a solution
polymerization process. Generally, manipulation of I.sub.10
/I.sub.2 while holding M.sub.w /M.sub.n relatively low for
producing the novel polymers described herein is a function of
reactor temperature and/or ethylene concentration. Surprisingly,
reduced ethylene concentration and higher temperature generally
produces higher I.sub.10 /I.sub.2. Generally, as the percent of
ethylene is converted into polymer, the ethylene concentration in
the reactor decreases and the polymer concentration increases. For
the novel substantially linear ethylene/alpha-olefin copolymers and
substantially linear ethylene homopolymers claimed herein, the
polymer concentration for a continuous solution polymerization
process is preferably above about 5 weight percent of the reactor
contents, especially above about 15 weight percent of the reactor
contents, and as high as about 40 weight percent of the reactor
contents. Typically greater than 70 percent, preferably greater
than 80 percent and more preferably greater than 90 percent, of the
ethylene is converted to polymer.
The substantially linear polymers of the present invention can be
ethylene homopolymers, or they can be interpolymers of ethylene
with at least one C.sub.3 -C.sub.20 alpha-olefin and/or C.sub.4
-C.sub.18 diolefins. The substantially linear polymers of the
present invention can also be interpolymers of ethylene with at
least one of the above C.sub.3 -C.sub.20 alpha-olefins and/or
diolefins in combination with other unsaturated monomers.
Monomers usefully copolymerized or interpolymerized with ethylene
according to the present invention include, for example,
ethylenically unsaturated monomers, conjugated or nonconjugated
dienes, polyenes, etc. Preferred comonomers include the C.sub.3
-C.sub.10 alpha-olefins especially propene, isobutylene, 1-butene,
1-hexene, 4-methyl-1-pentene, and 1-octene. Other preferred
monomers include styrene, halo- or allyl substituted styrenes,
vinylbenzocyclobutene, hexadiene, and naphthenics (e.g.,
cyclo-pentene, cyclo-hexene and cyclo-octene).
Other unsaturated monomers usefully copolymerized according to the
present invention include, for example, ethylenically unsaturated
monomers, conjugated or nonconjugated dienes, polyenes, etc.
Preferred comonomers include the C.sub.3 -C.sub.10 alpha-olefins
especially propene, isobutylene, 1-butene, 1-hexene,
4-methyl-1-pentene, and 1-octene. Other preferred comonomers
include styrene, halo- or alkyl substituted styrenes,
vinylbenzocyclobutene, 1,4-hexadiene, and naphthenics (e.g.,
cyclopentene, cyclohexene and cyclooctene).
The polymerization conditions for manufacturing the polymers of the
present invention are generally those useful in the solution
polymerization process, although the application of the present
invention is not limited thereto. Slurry and gas phase
polymerization processes are also believed to be useful, provided
the proper catalysts and polymerization conditions are
employed.
Multiple reactor polymerization processes are also useful in the
present invention, such as those disclosed in U.S. Pat. No.
3,914,342. The multiple reactors can be operated in series or in
parallel with at least one constrained geometry catalyst employed
in at least one of the reactors.
In general, the continuous polymerization according to the present
invention may be accomplished at conditions well known in the prior
art for Zeigler-Natta or Kaminsky-Sinn type polymerization
reactions, that is, temperatures from 0 to 250 C and pressures from
atmospheric to 1000 atmospheres (100 MPa). Suspension, solution,
slurry, gas phase or other process conditions may be employed if
desired. A support may be employed, but preferably the catalysts
are used in a homogeneous (i.e., soluble) manner. It will, of
course, be appreciated that the active catalyst system form in situ
if the catalyst and the cocatalyst components thereof are added
directly to the polymerization process and a suitable solvent or
diluent, including condensed monomer, is used in said
polymerization process. It is, however, preferred to form the
active catalyst in a separate step in a suitable solvent prior to
adding the same to the polymerization mixture.
The polymerization conditions for manufacturing the polymers of the
present invention are generally those useful in the solution
polymerization process, although the application of the present
invention is not limited thereto. Gas phase polymerization
processes are also believed to be useful, provided the proper
catalysts and polymerization conditions are employed.
Fabricated articles made from the novel ethylene polymers may be
prepared using all of the conventional polyethylene processing
techniques. Useful articles include films (e.g., cast, blown and
extrusion coated), fibers (e.g., staple fibers (including use of a
novel ethylene polymer disclosed herein as at least one component
comprising at least a portion of the fiber's surface), spunbond
fibers or melt blown fibers (using, e.g., systems as disclosed in
U.S. Pat. No. 4,340,563, U.S. Pat. No. 4,663,220, U.S. Pat. No.
4,668,566, or U.S. Pat. No. 4,322,027), and gel spun fibers (e.g.,
the system disclosed in U.S. Pat. No. 4,413,110)), both woven and
nonwoven fabrics (e.g., spun-laced fabrics disclosed in U.S. Pat.
No. 3,485,706) or structures made from such fibers (including,
e.g., blends of these fibers with other fibers, e.g., PET or
cotton) and molded articles (e.g., made using an injection molding
process, a blow molding process or a rotomolding process). The new
polymers described herein are also useful for wire and cable
coating operations, impact modification, especially at low
temperatures, of thermoplastic olefins (e.g., polypropylene), as
well as in sheet extrusion for vacuum forming operations, closed
cell and open cell foams including radiation and chemically
crosslinked foams and foam structures), and adhesives. All of the
preceding patents are incorporated herein by reference.
Useful compositions are also suitably prepared comprising the
substantially linear polymers of the present invention and at least
one other natural or synthetic polymer. Preferred other polymers
include thermoplastics such as styrene-butadiene block copolymers,
polystyrene (including high impact polystyrene), ethylene vinyl
acetate copolymers, ethylene acrylic acid copolymers, other olefin
copolymers (especially polyethylene copolymers) and homopolymers
(e.g., those polyethylene copolymers and homopolymers made using
conventional heterogeneous catalysts). Examples of such
heterogeneous polyethylene polymers and copolymers include polymers
made by the process of U.S. Pat. No. 4,076,698 (incorporated herein
by reference), other linear or substantially linear polymers of the
present invention, and mixtures thereof. Other substantially linear
polymers of the present invention and conventional heterogeneously
branched HDPE and/or heterogeneously branched LLDPE are preferred
for use in the thermoplastic compositions.
The compositions comprising the substantially linear ethylene
polymers are formed by any convenient method, including dry
blending the individual components and subsequently melt mixing,
either directly in the extruder used to make the finished article
(e.g., film), or by pre-melt mixing in a separate extruder. The
polyethylene compositions may also be prepared by multiple reactor
polymerization techniques. For example, one reactor may polymerize
the constrained geometry catalyzed polyethylene and another reactor
polymerize the heterogeneous catalyzed polyethylene, either in
series or in parallel operation.
Compositions comprising the ethylene polymers can also be formed
into fabricated articles such as those previously mentioned using
conventional polyethylene processing techniques which are well
known to those skilled in the art of polyethylene processing.
For examples described herein, unless otherwise stipulated, all
procedures were performed under an inert atmosphere of nitrogen or
argon. Solvent choices were often optional, for example, in most
cases either pentane or 30-60 petroleum ether can be interchanged.
Amines, silanes, lithium reagents, and Grignard reagents were
purchased from Aldrich Chemical Company. Published methods for
preparing tetramethylcyclopentadiene (C.sub.5 Me.sub.4 H.sub.2) and
lithium tetramethylcyclopentadiene (Li(C.sub.5 Me.sub.4 H)) include
C. M. Fendrick et al. Organometallics, 3, 819 (1984). Lithiated
substituted cyclopentadienyl compounds may be typically prepared
from the corresponding cyclopentadiene and a lithium reagent such
as n-butyl lithium. Titanium trichloride (TiCl.sub.3) was purchased
from Aldrich Chemical Company. The tetrahydrofuran adduct of
titanium trichloride, TiCl.sub.3 (THF).sub.3, was prepared by
refluxing TiCl.sub.3 in THF overnight, cooling, and isolating the
blue solid product, according to the procedure of L. E. Manzer,
Inorg. Syn., 21, 135 (1982).
EXAMPLES 1-4
The metal complex solution for Example 1 is prepared as
follows:
Part 1: Prep of Li(C.sub.5 Me.sub.4 H)
In the drybox, a 3 L 3-necked flask was charged with 18.34 g of
C.sub.5 Me.sub.4 H.sub.2, 800 mL of pentane, and 500 mL of ether.
The flask was topped with a reflux condenser, a mechanical stirrer,
and a constant addition funnel container 63 mL of 2.5 M n-BuLi in
hexane. The BuLi was added dropwise over several hours. A very
thick precipitate formed; approx. 1000 mL of additional pentane had
to be added over the course of the reaction to allow stirring to
continue. After the addition was complete, the mixture was stirred
overnight. The next day, the material was filtered, and the solid
was thoroughly washed with pentane and then dried under reduced
pressure. 14.89 g of Li(C.sub.5 Me.sub.4 H) was obtained (78
percent).
Part 2: Prep of C.sub.5 Me.sub.4 HSiMe.sub.2 Cl
In the drybox 30.0 g of Li(C.sub.5 Me.sub.4 H) was placed in a 500
mL Schlenk flask with 250 mL of THF and a large magnetic stir bar.
A syringe was charged with 30 mL of Me.sub.2 SiCl.sub.2 and the
flask and syringe were removed from the drybox. On the Schlenk line
under a flow of argon, the flask was cooled to -78 C, and the
Me.sub.2 SiCl added in one rapid addition. The reaction was allowed
to slowly warm to room temperature and stirred overnight. The next
morning the volatile materials were removed under reduced pressure,
and the flask was taken into the drybox. The oily material was
extracted with pentane, filtered, and the pentane was removed under
reduced pressure to leave the C.sub.5 Me.sub.4 HSiMeCl as a clear
yellow liquid (46.83 g; 92.9 percent).
Part 3: Prep of C.sub.5 Me.sub.4 HSiMeNH.sup.t Bu
In the drybox, a 3-necked 2 L flask was charged with 37.4 g of
t-butylamine and 210 mL of THF. C.sub.5 Me.sub.4 HSiMeCl (25.47 g)
was slowly dripped into the solution over 3-4 hours. The solution
turned cloudy and yellow. The mixture was stirred overnight and the
volatile materials removed under reduced pressure. The residue was
extracted with diethyl ether, the solution was filtered, and the
ether removed under reduced pressure to leave the C.sub.5 Me.sub.4
HSiMeNH.sup.t Bu as a clear yellow liquid (26.96 g; 90.8
percent).
Part 4: Prep of [MgCl].sub.2 [Me.sub.4 C.sub.5 SiMeN.sup.t
Bu](THF).sub.x
In the drybox, 14.0 mL of 2.0 M isopropylmagnesium chloride in
ether was syringed into a 250 mL flask. The ether was removed under
reduced pressure to leave a colorless oil. 50 mL of a 4:1 (by
volume) toluene:THF mixture was added followed by 3.50 g of
Me.sub.4 HC.sub.5 SiMe.sub.2 NH.sup.t Bu. The solution was heated
to reflux. After refluxing for 2 days, the solution was cooled and
the volatile materials removed under reduced pressure. The white
solid residue was slurried in pentane and filtered to leave a white
powder, which was washed with pentane and dried under reduced
pressure. The white powder was identified as [MgCl].sub.2 [Me.sub.4
C.sub.5 SiMe.sub.2 N.sup.t Bu](THF). (yield: 6.7 g).
Part 5: Prep of [C.sub.5 Me.sub.4 (SiMe.sub.2 N.sup.t
Bu)]TiCl.sub.2
In the drybox, 0.50 g of TiCl.sub.3 (THF).sub.3 was suspended in 10
mL of THF. 0.69 g of solid [MgCl].sub.2 [Me.sub.4 C.sub.5
SiMe.sub.2 N.sup.t Bu](THF).sub.x was added, resulting in a color
change from pale blue to deep purple. After 15 minutes, 0.35 g of
AgCl was added to the solution. The color immediately began to
lighten to a pale green/yellow. After 1.5 hours, the THF was
removed under reduced pressure to leave a yellow-green solid.
Toluene (20 mL) was added, the solution was filtered, and the
toluene was removed under reduced pressure to leave a yellow-green
solid, 0.51 g (quantitative yield) identified by 1H NMR as [C.sub.5
Me.sub.4 (SiMe.sub.2 N.sup.t Bu)]TiCl.sub.2.
Part 6: Preparation of [C.sub.5 Me.sub.4 (SiMe.sub.2 N.sup.t
Bu)]TiMe.sub.2
In an inert atmosphere glove box, 9.031 g of [C.sub.5 Me.sub.4
(Me.sub.2 SiN.sup.t Bu)]TiCl.sub.2 is charged into a 250 ml flask
and dissolved into 100 ml of THF. This solution is cooled to about
-25 C by placement in the glove box freezer for 15 minutes. To the
cooled solution is added 35 ml of a 1.4 M MeMgBr solution in
toluene/THF (75/25). The reaction mixture is stirred for 20 to 25
minutes followed by removal of the solvent under vacuum. The
resulting solid is dried under vacuum for several hours. The
product is extracted with pentane (4.times.50 ml) and filtered. The
filtrate is combined and the pentane removed under vacuum giving
the catalyst as a straw yellow solid.
The metal complex, [C.sub.5 Me.sub.4 (SiMe.sub.2 N.sup.t
Bu)]TiMe.sub.2, solution for Examples 2 and 3 is prepared as
follows:
In an inert atmosphere glove box 10.6769 g of a tetrahydrofuran
adduct of titanium trichloride, TiCl.sub.3 (THF).sub.3, is loaded
into a 1 L flask and slurried into 300 ml of THF. To this slurry,
at room temperature, is added 17.402 g of [MgCl].sub.2 [N.sup.t
BuSiMe.sub.2 C.sub.5 Me.sub.4 ] (THF).sub.x as a solid. An
additional 200 ml of THF is used to help wash this solid into the
reaction flask. This addition resulted in an immediate reaction
giving a deep purple solution. After stirring for 5 minutes 9.23 ml
of a 1.56 M solution of CH.sub.2 Cl.sub.2 in THF is added giving a
quick color change to dark yellow. This stage of the reaction is
allowed to stir for about 20 to 30 minutes. Next, 61.8 ml of a 1.4
M MeMgBr solution in toluene/THF (75/25) is added via syringe.
After about 20 to 30 minutes stirring time the solvent is removed
under vacuum and the solid dried. The product is extracted with
pentane (8.times.50 ml) and filtered. The filtrate is combined and
the pentane removed under vacuum giving the metal complex as a tan
solid.
The metal complex, [C.sub.5 Me.sub.4 (SiMe.sub.2 N.sup.t
Bu)]TiMe.sub.2, solution for Example 4 is prepared as follows:
In an inert atmosphere glove box 4.8108 g of TiCl.sub.3 (THF).sub.3
is placed in a 500 ml flask and slurried into 130 ml of THF. In a
separate flask 8.000 g of [MgCl].sub.2 [N.sup.t BuSiMe.sub.2
C.sub.5 Me.sub.4 ](THF).sub.x is dissolved into 150 ml of THF.
These flasks are removed from the glove box and attached to a
vacuum line and the contents cooled to -30 C. The THF solution of
[MgCl].sub.2 [N.sup.t BuSiMe.sub.2 C.sub.5 Me.sub.4 ](THF).sub.x is
transferred (over a 15 minute period) via cannula to the flask
containing the TiCl.sub.3 (THF).sub.3 slurry. This reaction is
allowed to stir for 1.5 hours over which time the temperature
warmed to 0 C and the solution color turned deep purple. The
reaction mixture is cooled back to -30 C and 4.16 ml of a 1.56 M
CH.sub.2 Cl.sub.2 solution in THF is added. This stage of the
reaction is stirred for an additional 1.5 hours and the temperature
warmed to -10 C. Next, the reaction mixture is again cooled to -40
C and 27.81 ml of a 1.4 M MeMgBr solution in tolene/THF (75/25) was
added via syringe and the reaction is now allowed to warm slowly to
room temperature over 3 hours. After this time the solvent is
removed under vacuum and the solid dried. At this point the
reaction flask is brought back into the glove box where the product
is extracted with pentane (4.times.50 ml) and filtered. The
filtrate is combined and the pentane removed under vacuum giving
the catalyst as a tan solid. The metal complex is then dissolved
into a mixture of C.sub.8 -C.sub.10 saturated hydrocarbons (e.g.,
Isopar.TM. E, made by Exxon) and ready for use in
polymerization.
Polymerization
The polymer products of Examples 1-4 are produced in a solution
polymerization process using a continuously stirred reactor.
Additives (e.g., antioxidants, pigments, etc.) can be incorporated
into the interpolymer products either during the pelletization step
or after manufacture, with a subsequent re-extrusion. Examples 1-4
are each stabilized with 1250 ppm calcium stearate, 200 ppm Irganox
1010, and 1600 ppm Irgafos 168. Irgafos.TM. 168 is a phosphite
stabilizer and Irganox.TM. 1010 is a hindered polyphenol stabilizer
(e.g., tetrakis [methylene
3-(3,5-ditert.butyl-4-hydroxyphenylpropionate)]methane. Both are
trademarks of and made by Ciba-Geigy Corporation. A representative
schematic for the polymerization process is shown in FIG. 1.
The ethylene (4) and the hydrogen are combined into one stream (15)
before being introduced into the diluent mixture (3). Typically,
the diluent mixture comprises a mixture of C.sub.8 -C.sub.10
saturated hydrocarbons (1), (e.g., Isopar.TM. E, made by Exxon) and
the comonomer(s) (2). For Example 1, the comonomer is 1-octene. The
reactor feed mixture (6) is continuously injected into the reactor
(9). The metal complex (7) and the cocatalyst (8) (the cocatalyst
is tris(pentafluorophenyl)borane for Examples 1-4 herein which
forms the ionic catalyst in situ) are combined into a single stream
and also continuously injected into the reactor. Sufficient
residence time is allowed for the metal complex and cocatalyst to
react to the desired extent for use in the polymerization
reactions, at least about 10 seconds. For the polymerization
reactions of Examples 1-4, the reactor pressure is held constant at
about 490 psig. Ethylene content of the reactor, after reaching
steady state, is maintained below about 8 percent.
After polymerization, the reactor exit stream (14) is introduced
into a separator (10) where the molten polymer is separated from
the unreacted comonomer(s), unreacted ethylene, unreacted hydrogen,
and diluent mixture stream (13). The molten polymer is subsequently
strand chopped or pelletized and, after being cooled in a water
bath or pelletizer (11), the solid pellets are collected (12).
Table I describes the polymerization conditions and the resultant
polymer properties:
TABLE I
__________________________________________________________________________
Example 1* 2 3 4
__________________________________________________________________________
Ethylene feed rate (lbs/hour) 3.2 3.8 3.8 3.8 Comonomer/Total
Olefin ratio* (mole percent) 12.3 0 0 0 Hydrogen/ethylene ratio
(mole percent) 0.054 0.072 0.083 0.019 Diluent/ethylene ratio
(weight basis) 9.5 7.4 8.7 8.7 Metal complex conc. 0.00025 0.005
0.001 0.001 (molar) Metal complex flow rate (ml/min) 5.9 1.7 2.4
4.8 Cocatalyst conc. 0.001 0.001 0.002 0.002 (molar) Cocatalyst
flow rate (ml/min) 2.9 1.3 6 11.9 Reactor temp (EC) 114 160 160 200
Polymer concentration (wt %) in the reactor exit 7.1 8.4 9.5 8.4
stream Comonomer concentration (wt %) in the reactor exit 3.8 0 0 0
stream Ethylene conc. in the reactor exit stream 2.65 3.59 0.86
1.98 (weight percent) Product I.sub.2 1.22 0.96 1.18 0.25 (g/10
minutes) Product density 0.903 0.954 0.954 0.953 (g/cm.sup.3)
Product I.sub.10 /I.sub.2 6.5 7.4 11.8 16.1 Single DSC Melting Peak
(C.) 97 132 131 132 Product M.sub.w 95,400 93,800 71,600 105,800
Product M.sub.n 50,000 48,200 34,200 51,100 Product M.sub.w
/M.sub.n 1.91 1.95 2.09 2.07 Ethylene Conversion (%) 71 70 92 81
LCB/Chain N.M.** -- 0.53 0.66 LCB/10,000 Carbons N.M.** -- 2.2 1.8
Aluminium Residue (ppm) 0 0 0 0
__________________________________________________________________________
*For Example 1, the Comonomer/Total Olefin ratio is defined as the
percentage molar ratio of 1octene/(1-octene + ethylene). Ex. 1* is
a Comparative Example since the copolymer has onset of gross melt
fracture less than 4 .times. 10.sup.6 dyne/cm.sup.2. **N.M. = Not
Measured.
The .sup.13 C NMR spectrum of Example 3 (ethylene homopolymer)
shows peaks which can be assigned to the alpha,delta.sup.+,
beta,delta.sup.+ and methine carbons associated with a long chain
branch. Long chain branching is determined using the method of
Randall described earlier in this disclosure, wherein he states
that "Detection of these resonances in high-density polyethylenes
where no 1-olefins were added during the polymerization should be
strongly indicative of the presence of long chain branching." Using
the equation 141 from Randall (p. 292):
wherein alpha=the average intensity of a carbon from a branch
(alpha,delta.sup.+) carbon and T.sub.Tot =the total carbon
intensity. The number of long chain branches in this sample is
determined to be 3.4 per 10,000 total carbon atoms, or 0.34 long
chain branches/1000 total carbon atoms using 300 MHz .sup.13 C NMR,
and 2.2 per 10,000 total carbon atoms, or 0.22 long chain
branches/1000 total carbon atoms using a 600 MHz .sup.13 C NMR.
EXAMPLES 5, 6 AND COMPARATIVE EXAMPLES 7-9
Examples 5,6 and Comparison Examples 7-9 with the same melt index
are tested for rheology Comparison. Examples 5 and 6 are the
substantially linear ethylene/1-octene copolymers produced by the
constrained geometry catalyst technology, as described in Example
1, with the exception that lower ethylene concentrations were used
for Examples 5 and 6 providing for higher I.sub.10 /I.sub.2 ratios
and consequently more long chain branching than Example 1. Examples
5 and 6 are stabilized as Examples 1-4. Comparison Examples 7, 8
and 9 are conventional heterogeneous Ziegler polymerization blown
film resins Dowlex.TM. 2045A, Attane.TM. 4201, and Attane.TM. 4403,
respectively, all of which are ethylene/1-octene copolymers made by
The Dow Chemical Company.
Comparative Example 7 is stabilized with 200 ppm Irganox.TM. 1010,
and 1600 ppm Irgafos.TM. 168 while Comparative Examples 8 and 9 are
stabilized with 200 ppm Irganox.TM. 1010 and 800 ppm PEPQ.TM..
PEPQ.TM. is a trademark of Sandoz Chemical, the primary ingredient
of which is believed to be
tetrakis-(2,4di-tertbutyl-phenyl)-4,4'biphenylphosphonite. A
comparison of the physical properties of each Example and
Comparative Example is listed in Table II.
TABLE II
__________________________________________________________________________
Comparative Comparative Comparative Property Ex. 5 Ex. 6 Example 7
Example 8 Example 9
__________________________________________________________________________
I.sub.2 1 1 1 1 0.76 (g/10 minutes) Density 0.92 0.902 0.92 0.912
0.905 (g/cm.sup.3) I.sub.10 /I.sub.2 9.45 7.61 7.8-8 8.2 8.7
Product M.sub.w 73,800 96,900 124,600 122,500 135,300 Product
M.sub.n 37,400 46,400 34,300 32,500 31,900 Product M.sub.w /M.sub.n
1.97 2.09 3.5-3.8 3.8 3.8-4.2 DSC Melt Peak(s) 111 95 114,118,122
100,116,121 96,116,121 (C.)
__________________________________________________________________________
Surprisingly, even though the molecular weight distribution of
Examples 5 and 6 is narrow (i.e., M.sub.w /M.sub.n is low), the
I.sub.10 /I.sub.2 values are comparable or higher in comparison
with Comparative Examples 7-9. A comparison of the relationship
between I.sub.10 /I.sub.2 vs. M.sub.w /M.sub.n for some of the
novel polymers described herein and conventional heterogeneous
Ziegler polymers is given in FIG. 2. The I.sub.10 /I.sub.2 value
for the novel polymers of the present invention is essentially
independent of the molecular weight distribution, M.sub.w /M.sub.n
which is not true for conventional Ziegler polymerized resins.
Example 5 and Comparative Example 7 with similar melt index and
density (Table II) are also extruded via a Gas Extrusion Rheometer
(GER) at 190 C using a 0.0296" diameter, 20:1 L/D die. The
processing index (P.I.) is measured at an apparent shear stress of
2.15.times.10.sup.6 dyne/cm.sup.2 as described previously. The
onset of gross melt fracture can easily be identified from the
shear stress vs. shear rate plot shown in FIG. 3 where a sudden
jump of shear rate occurs. A comparison of the shear state and
corresponding shear rates before the onset of gross melt fracture
is listed in Table III. It is particularly interesting that the PI
of Example S is more than 20 percent lower than the PI of
Comparative Example 7 and that the onset of melt fracture or
sharkskin for Example 5 is also at a significantly higher shear
stress and shear rate in comparison with the Comparative Example 7.
Furthermore, the Melt Tension (MT) as well as Elastic Modulus of
Example 5 are higher than that of Comparative Example 7.
Note that each of the Comparative Examples 7-9 has three distinct
melting peaks as measured by DSC, which is evidence of their
heterogeneous branching distribution. In contrast, the polymers of
Examples 5 and 6 have a single melting peak as measured by DSC
between the temperatures of -30 and 150 C which is evidence of the
homogeneity of the polymers branching distribution. Furthermore,
the single melting peaks of Examples 5 and 6 indicate that each
polymer is not a "blend" unlike the polymers disclosed in U.S. Pat.
No. 5,218,071.
TABLE III ______________________________________ Comparative
Property Example 5 Example 7 ______________________________________
I.sub.2 1 1 (g/10 minutes) I.sub.10 /I.sub.2 9.45 7.8-8 PI (kpoise)
11 15 Melt tension (gms) 1.89 1.21 Elastic modulus at 0.1 2425
882.6 rad/sec (dynes/cm.sup.2) OGMF*, critical shear rate >1556
936 (1/sec) (not observed) OGMF*, critical shear stress
.gtoreq.0.452 0.366 (MPa) (not observed) OSMF**, critical shear
rate >1566 about 628 (1/sec) (not observed) OSMF**, critical
shear stress .gtoreq.0.452 about 0.25 (MPa) (not observed)
______________________________________ *Onset of Cross Melt
Fracture. **Onset of Surface Melt Fracture.
Example 6 and Comparison Example 9 have similar melt index and
density, but Example 6 has lower I.sub.10 /I.sub.2 (Table IV).
These polymers are extruded via a Gas Extrusion Rheometer (GER) at
190 C using a 0.0296 inch diameter, 20:1 L/D die. The processing
index (PI) is measured at an apparent shear stress of
2.15.times.10.sup.6 dyne/cm.sup.2 as described previously.
TABLE IV ______________________________________ Comparative
Property Example 6 Example 9 ______________________________________
I.sub.2 1 0.76 (g/10 minutes) I.sub.10 /I.sub.2 7.61 8.7 PI
(kpoise) 14 15 Melt tension (gms) 1.46 1.39 Elastic modulus at 0.1
1481 1921 rad/sec (dynes/cm.sup.2) OGMF*, critical shear rate 1186
652 (1/sec) OGMF*, critical shear stress 0.431 0.323 (MPa) OSMF**,
critical shear rate about 764 about 402 (1/sec) OSMF**, critical
shear stress 0.366 0.280 (MPa)
______________________________________ *Onset of Gross Melt
Fracture. **Onset of Surface Melt Fracture.
The onset of gross melt fracture can easily be identified from the
shear stress vs. shear rate plot shown in FIG. 4 where a sudden
increase of shear rate occurs at an apparent shear stress of about
3.23.times.10.sup.6 dyne/cm.sup.2 (0.323 MPa). A comparison of the
critical shear stresses and corresponding critical shear rates at
the onset of gross melt fracture is listed in Table IV. The PI of
Example 6 is surprisingly about the same as Comparative Example 9,
even though the I.sub.10 /I.sub.2 is lower for Example 6. The onset
of melt fracture or sharkskin for Example 6 is also at a
significantly higher shear stress and shear rate in comparison with
the Comparative Example 9. Furthermore, it is also unexpected that
the Melt Tension (MT) of Example 6 is higher than that of
Comparative Example 9, even though the melt index for Example 6 is
slightly higher and the I.sub.10 /I.sub.2 is slightly lower than
that of Comparative Example 9.
COMPARATIVE EXAMPLES 10-19
Batch ethylene/1-octene polymerizations were conducted under the
following conditions:
Preparation of [HNEt.sub.3 ]+[MeB(C.sub.6 F.sub.5).sub.3 ]--
A 100 ml flask was charged with 1.00 gram of
tris(pentafluorophenyl)boron (1.95 mmol) and 70 ml of anhydrous
pentane. After dissolution, 1-5 ml of MeLi (1.4 M in diethyl ether,
2.1 mmol, 1.07 equiv) was added at 25 C via syringe. A milky white
mixture formed immediately and, after several minutes, two phases
formed. The mixture was stirred for 15 hr and then the upper layer
decanted. The viscous lower layer was washed twice with 30 ml of
pentane and concentrated in vacuo for 2 hours to give a clear,
colorless, viscous oil. Under nitrogen, the oil was quenched with a
40 ml of an aqueous 0.5 M HNEt.sub.3 Cl solution (20 mmol, 10
equiv) which had previously been cooled to 0 C. A white, gooey
precipitate formed instantly. After two minutes, the sold was
collected by filtration and washed twice with 20 ml of 0.5 M
HNEt.sub.3 Cl solution followed by two washings with distilled
water. The solid was dehydrated under high vacuum at 25 C for 15
hours to give a powdery white solid (0.77 grams, 63%) which was
identified as the desired triethylammonium
tris(pentafluorophenyl)methylborate salt.
Preparation of [HNEt.sub.3 ]+[(allyl)B(C.sub.6 F.sub.5).sub.3
]--
A 100 ml flask was charged with 1.00 gram of
tris(pentafluorophenyl)boron (1.95 mmol) and 40 ml of anhydrous
pentane. After dissolution, 2.05 ml of (allyl)MgBr (1.0 M in
diethyl ether, 2.05 mmol, 1.05 equiv) was added at 25 C via
syringe. A cloudy white mixture formed immediately and, after
several minutes, two phases formed. The mixture was stirred for 15
hr and then the upper layer decanted. The viscous lower layer was
washed twice with 30 ml of pentane and concentrated in vacuo for 2
hours to give a clear, colorless, viscous oil. Under nitrogen, the
oil was quenched with a 40 ml of an aqueous 0.5 M HNEt.sub.3 Cl
solution (20 mmol 10 equiv) which had previously been cooled to 0
C. A gooey, white precipitate formed after several minutes. The
solid was collected by filtration and washed twice with 20 ml of
0.5 MHNEt.sub.3 Cl solution followed by two washings with distilled
water. The solid was dehydrated under high vacuum at 25 C for 15
hours to give a pasty white solid (0.39 grams, 30%) which was
identified as the desired triethylammonium
tris(pentafluorophenyl)allylborate salt.
Batch Reactor Polymerization Procedure
A 2 L stirred autoclave was charged with the desired amounts of a
mixed alkane solvent (Isopar.RTM. E, available from Exxon
Chemicals, Inc.) and 1-octene comonomer. The reactor was heated to
the polymerization temperature. Hydrogen was added by differential
pressure expansion from a 75 ml addition tank.
The term "hydrogen delta psi" in Table 1 represents the difference
in pressure between the starting and final pressure in the hydrogen
addition tank after adding hydrogen to the 2 L reactor containing a
total of approximately 1200 ml of solvent and 1-octene. The reactor
was heated to the polymerization temperature and was saturated with
ethylene to the desired pressure. For these experiments, a constant
ethylene/solvent pressure of about 500 psig at a temperature of 140
C corresponds to an ethylene concentration of about 8.4 percent by
weight of the reactor contents. Metal complex and cocatalyst were
mixed in a drybox by syringing the desired amount of 0.0050 M metal
complex solution (in Isopar.RTM. E or toluene) into a solution of
the cocatalyst (in Isopar.RTM. E or toluene). This solution was
then transferred to a catalyst addition tank and injected into the
reactor. The polymerization was allowed to proceed for the desired
time and then the solution was drained from the bottom of the
reactor and quenched with isopropanol. About 100 mg of a hindered
phenolic antioxidant (Irganox.RTM. 1010, available from Ciba-Geigy
corporation) was added and the polymer was air dried overnight. The
residual solvent was removed in a vacuum oven overnight. The
results are shown in Table V and VA:
TABLE V ______________________________________ Comp. H.sub.2
1-octene Isopar yield Effcny. Aluminum Ex. (psi) (gms) E (gms)
(gms) (gm/gm Ti) (ppm) ______________________________________ 10A*
50 38 820 39.6 330,689 0 11A* 25 38 820 70.1 390,257 0 12A* 35 38
820 46.4 258,316 0 13A* 30 38 820 48.8 271,677 0 14A* 35 30 828
52.1 290,049 0 15A* 27 38 820 36.5 152,401 0 16A** 26 38 820 47.8
266,110 0 17B*** 35 40 818 19.7 41,127 6850 18B*** 50 40 818 19.7
41,127 6850 19B*** 25 40 818 18.3 38,204 7380
______________________________________ A = metal complex of
[(C.sub.5 Me.sub.4)SiMe.sub.2 2N(tBu)]TiMe.sub.2 (as in U.S. Pat.
No. 5,064,802) B = metal complex of [(C.sub.5 Me.sub.4)SiMe.sub.2
N(tBu)]TiCl.sub.2 (as in U.S. Pat. No. 5,026,798) *= Cocatalyst of
[Et.sub.3 NH] + [(allyl)B(C.sub.6 F.sub.5).sub.3 ] (as i U.S. Pat.
No. '802) **= Cocatalyst of [Et.sub.3 NH] + [(Me)B(C.sub.6
F.sub.5).sub.3 ] (as in U.S. Pat. No. '802) ***= methyl aluminoxane
(MAO) (as in U.S. Pat. No. '798) Reactor temperature is constant at
about 140 C. Ethylene/solvent pressure is constant at about 500
psig Run time is about 15 minutes
TABLE VA ______________________________________ .mu.moles .mu.moles
Irganox 1010 Comp. Ex. complex cocatalyst (ppm)
______________________________________ 10A* 2.5 2.5 2500 11A* 3.75
3.75 1400 12A* 3.75 3.75 2200 13A* 3.75 3.75 2000 14A* 3.75 3.75
1900 15A* 5 5 2700 16A* 3.75 3.75 2000 17B*** 10 5000 5000 18B***
10 5000 5000 19B*** 10 5000 5500
______________________________________ A = metal complex of
[(C.sub.5 Me.sub.4)SiMe.sub.2 N(tBu)] TiMe.sub.2 (as in USP
5,064,802) B = metal complex of [(C.sub.5 Me.sub.4)SiMe.sub.2
N(tBu)] TiCl.sub.2 (as in USP 5,026,798) *Cocatalyst of [Et.sub.3
NH] + [(allyl)B(C.sub.6 F.sub.5).sub.3 (as in USP `802)
**Cocatalyst of [Et.sub.3 NH] + [(Me)B(C.sub.6 F.sub.5).sub.3 (as
in USP `802) ***methyl aluminoxane (MAO) (as in USP `798) Reactor
temperature is constant at about 140 C. Ethylene/solvent pressure
is constant at about 500 psig Run time is about 15 minutes
The samples were each extruded via a Gas Extrusion Rheometer (GER)
at 190 C using 0.0296 inch diameter die (preferably 0.0143 inch
diameter die for high flow polymers, e.g. 50-100 MI or greater)
having L/D of 20:1 and entrance angle of 180 degrees, as shown in
the attached drawing. The OGMF can easily be identified from the
shear stress vs. shear rate plot where a sudden jump of shear rate
occurs or when the surface of the extrudate becomes very rough or
irregular, or from deep ridges which can be clearly detected by
visual observation. OSMF is characterized by fine scale surface
irregularities ranging from loss of surface gloss to the more
severe form of matte or sharksldn which can easily be seen using
microscopy at a magnification of 40.times..
Table VI displays the test results from Comparative Examples
10-19:
TABLE VI ______________________________________ OGMF* OGMF* I.sub.2
Shear Shear Comp. (gm/ Measured Rate Stress Ex. 10 min) I.sub.10
/I.sub.2 (I.sub.10 /I.sub.2) - 4.63 M.sub.w /M.sub.o (sec.sup.-1)
(MPa) ______________________________________ 10 4.52 5.62 0.99
1.856 706 0.344 11 0.67 6.39 1.76 1.834 118 0.323 12 2.24 5.62 0.99
1.829 300 0.323 13 2.86 5.60 0.97 1.722 397 0.323 14 3.25 5.66 1.03
1.827 445 0.302 15 1.31 5.67 1.04 1.718 227 0.302 16 1.97 5.7 1.07
1.763 275 0.302 17 0.36 12.98 8.35 5.934 <29 <0.086 18 0.40
13.34 8.71 5.148 <11.08 <0.086 19 0.13 13.25 8.62 6.824
<10.39 <0.086 ______________________________________
Comparative Examples 10-16 were prepared using the catalyst
composition as described in U.S. Pat. No. 5,064,802 (Stevens et
al.) as described above. Comparative Examples 17-19 were prepared
using the catalyst composition described in U.S. Pat. No. 5,026,798
(Canich), as described above. All of the Comparative Polymer
Examples made using a batch reactor at an ethylene concentration of
about 8.4 percent by weight of the reactor contents or more tested
had onset of gross melt fracture at a shear stress of less than or
equal to 0.344 MPa (3.44.times.10.sup.6 dyne/cm.sup.2).
Interestingly, an ethylene concentration of about 8.4 percent is
considered to be on the low side for a batch polymerization
procedure, since it limits the reaction kinetics and slows the
polymerization process. Increasing the ethylene concentration in a
batch reactor, as is taught in U.S. Pat. No. 5,026,798 (Canich),
where the calculated propylene reactor concentrations for these ten
examples ranges from a low of about 12.6 percent (Example 1) to a
high of about 79 percent (Example 6), by weight of the reactor
contents, results in polymerization of polymers which do not have
the novel structure discovered by Applicants, as the OGMF data in
Table VI demonstrates. Furthermore, the I.sub.10 /I.sub.2 ratio of
such comparative polymers made using a batch reactor at relatively
high ethylene concentrations increases as the molecular weight
distribution, M.sub.w /M.sub.n, increases, as is expected based on
conventional Ziegler polymerized polymers.
EXAMPLE 20 AND COMPARATIVE EXAMPLE 21
Blown film is fabricated from the two novel ethylene/1-octene
polymers of Examples 5 and 6 made in accordance with the present
invention and from two comparative conventional polymers made
according to conventional Ziegler catalysis. The blown films are
tested for physical properties, including heat seal strength versus
heat seal temperature (shown in FIG. 5 for Examples 20 and 22 and
Comparative Examples 21 and 23), machine (MD) and cross direction
(CD) properties (e.g., tensile yield and break, elongation at break
and Young's modulus). Other film properties such as dart, puncture,
tear, clarity, haze, 20 degree gloss and block are also tested.
Blown Film Fabrication Conditions
The improved processing substantially linear polymers of the
present invention produced via the procedure described earlier, as
well as two comparative resins are fabricated on an Egan blown film
line using the following fabrication conditions:
2 inch (5 cm) diameter extruder
3 inch (7.6 cm) die
30 mil die gap
25 RPM extruder speed
460 F (238 C) melt temperature
1 mil gauge
2.7:1 Blow up ratio (12.5 inches (31.7 cm) layflat)
12.5 inches (31.7 cm) frost line height
The melt temperature is kept constant by changing the extruder
temperature profile. Frost line height is maintained at 12.5 inches
(31.7 cm) by adjusting the cooling air flow. The extruder output
rate, back pressure and power consumption in amps are monitored
throughout the experiment. The polymers of the present invention
and the comparative polymers are all ethylene/1-octene copolymers.
Table VII summarizes physical properties of the two polymers of the
invention and for the two comparative polymers:
TABLE VII ______________________________________ Comparative
Comparative Property Example 20 Example 21 Example 22 Example 23
______________________________________ I.sub.2 (g/10 1 1 1 0.8
minutes) Density 0.92 0.92 0.902 0.905 (g/cm.sup.3) I.sub.10
/I.sub.2 9.45 about 8 7.61 8.7 M.sub.w /M.sub. 1.97 about 4 2.09
about 5 ______________________________________
Tables VIII and IX summarize the film properties measured for blown
film made from two of these four polymers:
TABLE VIII ______________________________________ Blown film
properties Comparative Comparative Example Example Example Example
Property 20 MD 20 CD 21 MD 21 CD
______________________________________ Tensile yield 1391 1340 1509
1593 (psi) Tensile break 7194 5861 6698 6854 (psi) Elongation 650
668 631 723 (percent) Young's 18,990 19,997 23,086 23,524 modulus
(psi) PPT* tear 5.9 6.8 6.4 6.5 (gms)
______________________________________ *Puncture Propagation Tear
MD = machine direction CD = cross direction
TABLE IX ______________________________________ Comparative
Property Example 20 Example 21
______________________________________ Dart A (grams) 472 454
Puncture (grams) 235 275 Clarity (percent transmittance) 71 68 Haze
(percent) 3.1 6.4 20 degree gloss 114 81 Block (grams) 148 134
______________________________________
During the blown film fabrication, it is noticed that at the same
screw speed (25 rpm) and at the same temperature profile, the
extruder back pressure is about 3500 psi at about 58 amps power
consumption for Comparative Example 21 and about 2550 psi at about
48 amps power consumption for Example 20, thus showing the novel
polymer of Example 20 to have improved processability over that of
a conventional heterogeneous Ziegler polymerized polymer. The
throughput is also higher for Example 20 than for Comparative
Example 21 at the same screw speed. Thus, Example 20 has higher
pumping efficiency than Comparative Example 21 (i.e., more polymer
goes through per turn of the screw).
As FIG. 5 shows, the heat seal properties of polymers of the
present invention are improved, as evidenced by lower heat seal
initiation temperatures and higher heat seal strengths at a given
temperature, as compared with conventional heterogeneous polymers
at about the same melt index and density.
EXAMPLES 24 AND 25
The polymer products of Examples 24 and 25 are produced in a
continuous solution polymerization process using a continuously
stirred reactor, as described in copending U.S. Pat. No. 5,272,236.
The metal complex [C.sub.5 Me.sub.4 (SiMe.sub.2 N.sup.t Bu)]TiMe is
prepared as described in U.S. Pat. No. 5,272,236 and the
cocatalysts used are tris(pentafluorophenyl) borane (B:Ti ratio of
2:1) and MMAO (Al:Ti ratio of 4:1). For Example 24 the ethylene
concentration in the reactor is about 1.10 percent and for Example
25 the ethylene concentration in the reactor is about 1.02 percent
(percentages based on the weight of the reactor contents). For each
Example, the reactor is run without hydrogen.
Additives (e.g., antioxidants, pigments, etc.) can be incorporated
into the interpolymer products either during the pelletization step
or after manufacture, with a subsequent re-extrusion. Examples 24
and 25 are each stabilized with 1250 ppm Calcium Stearate, 200 ppm
Irganox 1010, and 1600 ppm Irgafos 168. Irgafos.TM. 168 is a
phosphite stabilizer and Irganox.TM. 1010 is a hindered polyphenol
stabilizer (e.g., tetrakis [methylene
3-(3,5-ditert.butyl-4-hydroxyphenylpropionate)]methane. Both are
trademarks of and made by Ciba-Geigy Corporation.
EXAMPLE 24 AND COMPARATIVE EXAMPLE 26
Example 24 is an ethylene/1-octene elastic substantially linear
ethylene polymer produced as described herein.
Comparative Example 26 is an ethylene/1-butene copolymer
trademarked Exact.TM. made by Exxon Chemical containing butylated
hydroxy toluene (BHT) and Irganox.TM. 1076 as polymeric
stabilizers. Table X summarizes physical properties and rheological
performance of Example 24 and Comparative Example 26:
TABLE X ______________________________________ Comparative Property
Example 24 Example 26 ______________________________________
I.sub.2 (g/10 minutes) 3.3 3.58 Density (g,cm.sup.3) 0.870 0.878
I.sub.10 /I.sub.2 7.61 5.8 M.sub.w /M.sub.n 1.97 1.95 PI (kPoise)
3.2 8.4 Elastic Modulus @ 0.1 rad/sec 87.7 8.3 (dyne/cm.sup.2)
OSMF*, critical shear rate 660 250 (sec.sup.-1)
______________________________________ *Onset of surface melt
fracture
Even though Example 24 and Comparative Example 26 have very similar
molecular weight distributions (M.sub.w /M.sub.n), 2 and density,
Example 24 has a much lower processing index (PI) (38 percent of
the PI of Comparative Example 26), a much higher shear rate at the
onset of surface melt fracture (264 percent of shear rate at onset
of OSMF) and an elastic modulus an order of magnitude higher than
Comparative Example 26, demonstrating that Example 24 has much
better processability and higher melt elasticity than Comparative
Example 26.
Elastic modulus is indicative of a polymer's melt stability, e.g.,
more stable bubbles when making blown film and less neck-in during
melt extrusion. Resultant physical properties of the finished film
are also higher.
Onset of surface melt fracture is easily identified by visually
observing the surface extrudate and noting when the extrudate
starts losing gloss and small surface roughness is detected by
using 40.times. magnification.
Dynamic shear viscosity of the polymers is also used to show
differences between the polymers and measures viscosity change
versus shear rate. A Rheometrics Mechanical Spectrometer (Model RMS
800) is used to measure viscosity as a function of shear rate. The
RMS 800 is used at 190 C at 15 percent strain and a frequency sweep
(i.e., from 0.1-100 rad/sec) under a nitrogen purge. The parallel
plates are positioned such that they have a gap of about 1.5-2 mm.
Data for Example 24 and Comparative Example 26 are listed in Table
XI and graphically displayed in FIG. 6.
TABLE XI ______________________________________ Dynamic Viscosity
Shear Rate Dynamic Viscosity (poise) (poise) for Comparative
(rad/sec) for Example 24 Example 26
______________________________________ 0.1 28290 18990 0.1585 28070
18870 0.2512 27630 18950 0.3981 27140 18870 0.631 26450 18840 1
25560 18800 1.585 24440 18690 2.512 23140 18540 3.981 21700 18310
6.31 20170 17960 10 18530 17440 15.85 16790 16660 25.12 14960 15620
39.81 13070 14310 63.1 11180 12750 100 9280 10960
______________________________________
Surprisingly, Example 24 shows a shear thinning behaviour, even
though Example 24 has a narrow molecular weight distribution. In
contrast, Comparative Example 26 shows the expected behaviour of a
narrow molecular weight distribution polymer, with a flatter
viscosity/shear rate curve.
Thus, elastic substantially linear ethylene polymers made in
accordance with the present invention (e.g. Example 24) have lower
melt viscosity than a typical narrow molecular weight distribution
linear copolymer made by single site catalyst technology at the
melt processing shear rate region of commercial interest In
addition, the novel elastic substantially linear ethylene polymers
have a higher low shear/zero shear viscosity than the Comparative
linear polymer, thus demonstrating that the copolymers of the
invention have higher "green strength" which is useful for forming
and maintaining blended compositions such as those used in the wire
and cable coating industry, where the compounded materials must
maintain their integrity at low or zero shear without segregating
the components.
EXAMPLE 25 AND COMPARATIVE EXAMPLE 27
Example 25 is an ethylene/1-octene elastic substantially linear
ethylene polymer produced in a continuous solution polymerization
process as described herein.
Comparative Example 27 is an ethylene/propene copolymer made by
Mitsui PetroChemical Corporation and trademarked Tafmer.TM. P-0480.
Table XII summarizes physical properties and rheological
performance of these two polymers:
TABLE XII ______________________________________ Comparative
Property Example 25 Example 27
______________________________________ I.sub.2 (g/10 minutes) 1.01
1.1 Density (g/cm.sup.3) 0.870 0.870 I.sub.10 /I.sub.2 7.62 6.06
M.sub.w M.sub.n 1.98 1.90 PI (kPoise) 7.9 27.4 Elastic Modulus @
0.1 964 567.7 rad/sec (dyne/cm.sup.2) OSMF*, critical shear rate
781 105 (sec.sup.-1) ______________________________________ *Onset
of surface melt fracture
Even though Example 25 and Comparative Example 27 have similarly
narrow molecular weight distributions (M.sub.w /M.sub.n), I.sub.2,
and density, Example 25 has a PI which is 28 percent of that of
Comparative Example 27, a 743 percent of the shear rate at the
onset of surface melt fracture and a higher elastic modulus than
Comparative Example 27, demonstrating that Example 24 has much
better processability than Comparative Example 27. Onset of surface
melt fracture is easily identified by visually observing the
surface extrudate and noting when the extrudate starts losing gloss
and small surface roughness is detected by using 40.times.
magnification.
EXAMPLES 28-37
Examples 28-35 are ethylene/propene copolymers made using the
constrained geometry catalyst described herein and in a continuous
solution polymerization process. Examples 36 and 37 are
ethylene/1-butene copolymers made using the constrained geometry
catalyst described herein and in a continuous solution
polymerization process. Examples 28-37 each contained approximately
1250 ppm calcium stearate, 200 ppm Irganox 1010. These polymers did
not, however, contain a secondary antioxidant (e.g. a phosphite).
The low level of phenol (ie. 200 ppm Irganox 1010) coupled with the
lack of the secondary antioxidant may have contributed to the lower
melt fracture performance of some of the polymers shown in Table
XV. It is well known that thermally processing polyethylene
polymers, especially in the presence of oxygen, can lead to
oxidative crosslinking and extrusion variation, i.e. melt fracture.
Table XIII and XIIIA describe the polymerization conditions and
Table XIV describes the resultant polymer physical properties for
Examples 28-35:
TABLE XIII ______________________________________ Reactor ethylene
Estimated conc. reactor PE Hydrogen/ (weight conc. (weight Ethylene
flow ethylene ratio Ex. percent) percent) fate (lbs/hr) (mole
percent) ______________________________________ 28 5.3 6.0 3.19
0.048 29 4.2 7.3 3.19 0.024 30 4.0 8.9 3.19 0.028 31 3.5 9.3 3.18
0.024 32 2.5 10.6 3.20 0.027 33 2.6 10.7 3.18 0.007 34 1.3 10.5
3.19 0.027 35 1.0 10.9 3.19 0.010
______________________________________
TABLE XIIIA ______________________________________ Diluent/
Ethylene ethylene Comonomer/olefin Ex. Reactor temp (C.) Conversion
% ratio ratio* ______________________________________ 28 170 51 8.2
25.5 29 172 61 8.1 24.0 30 171 67 7.1 16.6 31 171 71 7.2 20.1 32
170 79 7.1 15.6 33 173 78 7.1 16.7 34 145 88 8.2 17.8 35 158 91 8.2
18.8 ______________________________________ *Comonomer/total olefin
ratio = percentage weight ratio of propene/(propene +
ethylene).
TABLE XIV ______________________________________ I.sub.2 (gms/10
Density Ex. minutes) I.sub.10 /I.sub.2 (gm/cm.sup.3) M.sub.w
/M.sub.n ______________________________________ 28 1.08 7.8 0.9176
2.00 29 1.02 8.8 0.9173 2.17 30 0.82 9.2 0.9175 2.08 31 0.79 9.4
0.9196 2.04 32 1.01 10.6 0.9217 2.09 33 0.83 12.4 0.9174 2.31 34
0.54 15.2 0.9201 2.12 35 0.62 15.6 0.9185 2.32
______________________________________
FIG. 7 graphically displays a best fit line drawn through a plot of
the I.sub.10 /I.sub.2 ratio for the ethylene/propene substantially
linear polymers of Examples 28-35 as a function of ethylene
concentration in the polymerization reactor. Surprisingly, in
contrast to conventional Ziegler polymerized polymers and in
contrast to a batch polymerization using the same catalyst and
relatively high ethylene concentrations, as the ethylene
concentration in the reactor decreases using a continuous
polymerization process, the I.sub.10 /I.sub.2 ratio (indicating the
amount of long chain branching in the novel substantially linear
polymers) increases, even though the molecular weight distribution,
M.sub.w /M.sub.n, remains very narrow and essentially constant at
about 2.
Table 15 shows the critical shear stress and critical shear rate at
OGMF and OSMF for Examples 28-35:
TABLE XV ______________________________________ Example OSMF OGMF
______________________________________ 28 (shear stress) 2.15
.times. 10.sup.6 dyne/cm.sup.2 4.09 .times. 10.sup.6 dyne/cm.sup.2
28 (shear rate) 129.8 sec.sup.-1 668.34 sec.sup.-1 29 (shear
stress) 1.94 .times. 10.sup.6 dyne/cm.sup.2 4.3 .times. 10.sup.6
dyne/cm.sup.2 29 (shear rate) 118.8 sec.sup.-1 652.1 sec.sup.-1 30
(shear stress) 1.08 .times. 10.sup.6 dyne/cm.sup.2 4.3 .times.
10.sup.6 dyne/cm.sup.2 30 (shear rate) 86.12 sec.sup.-1 650.7
sec.sup.-1 31 (shear stress) 1.08 .times. 10.sup.6 dyne/cm.sup.2
>4.3 .times. 10.sup.6 dyne/cm.sup.2 31 (shear rate) 90.45
sec.sup.-1 >6.83 sec.sup.-1 32 (shear stress) 1.94 .times.
10.sup.6 dyne/cm.sup.2 3.66 .times. 10.sup.6 dyne/cm.sup.2 32
(shear rate) 178.2 sec.sup.-1 673 sec.sup.-1 33 (shear stress) 2.15
.times. 10.sup.6 dyne/cm.sup.2 about 3.23 .times. 10.sup.6
dyne/cm.sup.2 33 (shear rate) 235.7 sec.sup.-1 about 591 sec.sup.-1
34 (shear stress) 1.94 .times. 10.sup.6 dyne/cm.sup.2 3.44 .times.
10.sup.6 dyne/cm.sup.2 34 (shear rate) 204.13 sec.sup.-1 725.23
sec.sup.-1 35 (shear stress) 1.94 .times. 10.sup.6 dyne/cm.sup.2
about 3.26 .times. 10.sup.6 dyne/cm.sup.2 35 (shear rate) 274.46
sec.sup.-1 637.7 sec.sup.-1
______________________________________
Table XVI and XVIA describe the polymerization conditions and Table
XVII describes the resultant polymer physical properties for
ethylene-1-butylene copolymer Examples 36 and 37:
TABLE XVI ______________________________________ Reactor ethylene
Reactor PE conc. conc Hydrogen/ (weight (weight Ethylene flow
ethylene ratio Ex. percent) percent) rate (lbs/hr) (mole percent)
______________________________________ 36 5.3 5.8 3.20 0.035 37 1.3
10.8 3.19 0.010 ______________________________________
TABLE XVIA ______________________________________ Ethylene Comonom
Diluent/ Conversion er/olefin Ex. Reactor temp (C.) Ethylene Ratio
(%) ratio* ______________________________________ 36 170 8.1 51
24.2 37 152 8.2 87 17.1 ______________________________________
*Comonomer/total olefin ratio = percentage weight ratio of
1butene/(1-butene + ethylene).
TABLE XVII ______________________________________ I.sub.2 (gms/10
Density Ex. minutes) I.sub.10 /I.sub.2 (gm/cm.sup.3) M.sub.w
/M.sub.n ______________________________________ 36 0.59 7.5 0.9201
2.06 37 1.03 11.4 0.9146 2.22
______________________________________
The data in Tables XVI, XVIA and XVII show that as the ethylene
concentration in the reactor decreases while using the constrained
geometry catalyst as described herein, the I.sub.10 /I.sub.2 ratio
of the novel substantially linear polymers increases, indicating
the amount of long chain branching in the novel polymers, even
while the molecular weight distribution, M.sub.w /M.sub.n, of the
novel polymers remains narrow at essentially about 2.
Table XVII shows the critical shear stress and critical shear rate
at OGMF and OSMF for Examples 36 and 37:
TABLE XVIII ______________________________________ Example OSMF
OGMF ______________________________________ 36 (shear stress) 1.94
.times. 10.sup.6 dyne/cm.sup.2 4.09 .times. 10.sup.6 dyne/cm.sup.2
36 (shear rate) 52.3 sec.sup.-1 234.45 sec.sup.-1 37 (shear stress)
1.08 .times. 10.sup.6 dyne/cm.sup.2 3.01 .times. 10.sup.6
dyne/cm.sup.2 37 (shear rate) 160.5 sec.sup.-1 493.9 sec.sup.-1
______________________________________
COMPARATIVE EXAMPLE 38
An ethylene polymer, as described in U.S. Pat. No. 5,218,071, is
polymerized according to the teachings of that patent and tested
for melt fracture properties.
All catalyst manipulations were performed under anhydrous,
anaerobic conditions in an inert atmosphere box. The solvents,
toluene and Isopar E, and the comonomer, octene-1, were thoroughly
dried and deaerated before use. poly(methylalumioxane) (PMAO) was
obtained from AKZO Chemicals Inc. as a 1.55 M A1 in toluene
solution and used as received. The metallocene
ethylenebis(indenyl)hafnium dichloride was obtained rom Schering
A.G. as a solid. This metallocene is known to contain 0.2 weight
percent Zirconium contamination. A slurry of the hafnium complex
was prepared from this solid (0.253 g; 0.5 mmol; 0.010 M) and 50 mL
toluene. The slurry was thoroughly stirred overnight prior to
use.
A one gallon, stirred autoclave reactor was charged with Isopar E
(2.1 L) and octene-1 (175 mL) and the contents heated to 80 C. Upon
reaching temperature, a sample of the PMAO (26.8 mL; 40.0 mmol A1)
in toluene was pressured into the reactor from a 75 mL cylinder
using a nitrogen flush. After a few minutes, an aliquot of the
metallocene slurry (4.0 mL; 0.040 mmol; A1:Hf=1000:1) was flushed
into the reactor in a similar manner. Ethylene was continuously
supplied to the reactor at a rate of 17 g/min to initiate
polymerization. The ethylene flow was maintained for ten minutes
and during the latter part of the polymerization the flow rate
slowed as the pressure approached a setpoint of 100 psig. After
this time, the ethylene supply was shut off and the contents of the
reactor transferred by pressure to a glass resin kettle containing
a small amount of antioxidant (0.30 g Irgaphos 168; 0.07 g Irganox
1010). The solvent was slowly allowed to evaporate and the polymer
obtained form the solution was dried under vacuum at 50 C for 72 h.
The yield of the product was 159 g or an efficiency of 3975 g
PE/mmol Hf.
The recovered polymer had a MW=1.341.times.10.sup.5, M.sub.n
=5.65.times.10.sup.4, M.sub.w /M.sub.n =2.373, density (measured in
a gradient column)=0.8745 g/cc, I.sub.2 =0.63 g/10 min., I.sub.10
/I.sub.2 =15.9, and had two distinct melting peaks (as shown in
FIG. 8). The polymer showed two peak melting points, one at 30.56 C
and the other at 102.55 C. The polymer also showed two peak
crystallization points, one at 9.47 C and the other at 81.61 C.
Melt fracture was determined using the GER at 190 C with a die
having a diameter of 0.0145 inches and an L/D=20.
* * * * *